diff --git a/.gitignore b/.gitignore
index aa4950f..4c47a94 100644
--- a/.gitignore
+++ b/.gitignore
@@ -267,3 +267,4 @@ __pycache__/
 
 libs/
 libs.fixed/
+*/*.swp
diff --git a/README.md b/README.md
index 5ce6626..cb6c27c 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,9 @@
    - Make all simgame room transitions instant.
 - RemovedContractsFix
    - This fix removes invalid contracts allowing saves to load if a user created contract was removed from the mods in use.
+- NavigationMapFilterLagFix
+   - This fix removes some unnecessary code in the navigation map's difficulty filter selection.
+   - The performance gain is negligible in vanilla, but in modpacks using the entire IS map such as RT or BTA, this saves a few seconds.
 
 # Experimental patches
 - MDDB_TagsetQueryInChunks
diff --git a/source/BattletechPerformanceFix.csproj b/source/BattletechPerformanceFix.csproj
index 4c46833..dd24718 100644
--- a/source/BattletechPerformanceFix.csproj
+++ b/source/BattletechPerformanceFix.csproj
@@ -53,6 +53,7 @@
     <Compile Include="LocalizationPatches.cs" />
     <Compile Include="HarmonyPatches.cs" />
     <Compile Include="ContractLagFix.cs" />
+    <Compile Include="NavigationMapFilterLagFix.cs" />
     <Compile Include="DisableSensitiveDataLogDump.cs" />
     <Compile Include="DisableDeployAudio.cs" />
     <Compile Include="DisableSimAnimations.cs" />
@@ -67,7 +68,7 @@
     <Compile Include="LoadFixes.cs" />
     <Compile Include="ShaderDependencyOverride.cs" />
     <Compile Include="ShopTabLagFix.cs" />
-    <Compile Include="PatchMechLabLimitItems.cs" />
+    <Compile Include="PatchMechlabLimitItems.cs" />
     <Compile Include="EnableLoggingDuringLoads.cs" />
     <Compile Include="RemovedFlashpointFix.cs" />
     <Compile Include="RemovedContractsFix.cs" />
@@ -120,4 +121,4 @@
     <PostBuildEvent Condition="$(IsLinux) == true">yes | cp "$(TargetDir)$(TargetName).dll" "$(SolutionDir)../../Mods/BattletechPerformanceFix/$(TargetName).dll"</PostBuildEvent>
     <PostBuildEvent Condition="$(IsOSX) == true">yes | cp "$(TargetDir)$(TargetName).dll" "$(SolutionDir)../../Mods/BattletechPerformanceFix/$(TargetName).dll"</PostBuildEvent>
   </PropertyGroup>
-</Project>
\ No newline at end of file
+</Project>
diff --git a/source/Main.cs b/source/Main.cs
index 0231c9e..8c0785a 100644
--- a/source/Main.cs
+++ b/source/Main.cs
@@ -91,6 +91,7 @@ public static void Start(string modDirectory, string json)
                     { typeof(DataLoaderGetEntryCheck), true },
                     { typeof(ShopTabLagFix), true },
                     { typeof(ContractLagFix), true },
+                    { typeof(NavigationMapFilterLagFix), true },
                     { typeof(EnableLoggingDuringLoads), true },
                     { typeof(ExtraLogging), true },
                     { typeof(ShaderDependencyOverride), true },
diff --git a/source/NavigationMapFilterLagFix.cs b/source/NavigationMapFilterLagFix.cs
new file mode 100644
index 0000000..b3d43ab
--- /dev/null
+++ b/source/NavigationMapFilterLagFix.cs
@@ -0,0 +1,60 @@
+using System.Collections.Generic;
+using System.Linq;
+using BattleTech.UI;
+using Harmony;
+using System.Reflection;
+using System.Reflection.Emit;
+using static BattletechPerformanceFix.Extensions;
+
+namespace BattletechPerformanceFix
+{
+    /* Removes a redundant call for creating difficulty callouts, saves a few seconds per filter selection */
+    class NavigationMapFilterLagFix : Feature
+    {
+        public void Activate()
+        {
+            var method = AccessTools.Method(typeof(SGNavigationScreen), "OnDifficultySelectionChanged");
+            var transpiler = new HarmonyMethod(typeof(NavigationMapFilterLagFix), nameof(Transpiler));
+            Main.harmony.Patch(method, null, null, transpiler);
+        }
+        
+        // cuts out the if/else block in OnDifficultySelectionChanged() because CreateDifficultyCallouts()
+        // is called later by RefreshSystemIndicators() anyways just after the block
+        private static IEnumerable<CodeInstruction> Transpiler(IEnumerable<CodeInstruction> instructions)
+        {
+            int startIndex = -1;
+            int endIndex = -1;
+
+            // searches for the if block start & end points, in case some other mod is modifying this function
+            // (which is why we don't hardcode the indices)
+            var code = instructions.ToList();
+            for (int i = 0; i < code.Count-1; i++) {
+                if (startIndex == -1) {
+                    if (code[i].opcode == OpCodes.Ldarg_1 && code[i+1].opcode == OpCodes.Brtrue) {
+                        startIndex = i;
+                    }
+                } else {
+                    if (code[i].opcode == OpCodes.Ldarg_1 && code[i+1].opcode == OpCodes.Call &&
+                        (code[i+1].operand as MethodInfo).Name == "CreateDifficultyCallouts") {
+                        endIndex = i+1;
+                        break;
+                    }
+                }
+            }
+
+            if (startIndex != -1 && endIndex != -1) {
+                LogDebug("Overwriting instructions in SGNavigationScreen.OnDifficultySelectionChanged()" +
+                        " at indices " + startIndex + "-" + endIndex + " with nops");
+                for (int i = startIndex; i <= endIndex; i++) {
+                    code[i].opcode = OpCodes.Nop;
+                }
+            } else {
+                LogError("Failed to find the code to overwrite in " +
+                         "SGNavigationScreen.OnDifficultySelectionChanged(); no changes were made.");
+                LogError("NavigationMapFilterLagFix has not been applied, report this as a bug");
+            }
+
+            return code.AsEnumerable();
+        }
+    }
+}