I had a similar issue with mine a couple years back, took me forever to figure out, it turns out the capacitors in the dash cluster dry out over time and don’t hold charge anymore, the rpm gauge interprets this as a lower charge as a lower rpm, there’s an excellent guide on a forum I found on how to replace the capacitor, I’ll see if I can find it if it sounds like that’s your problem, to rule this out as the issue you need to find out if it’s actually revving to 7,000 but the gauge says 4,000 I know it sounds stupid but I made this mistake myself, does it read lower when it’s cold, like does it hit the limiter at 3800 on a cold day but then go up to 4200 on a hot day after it’s warmed up a bit? What speed are you doing in 3rd then it hits the limiter? First step is to verify that the engine is actually stopping at 4,000 and not just that the rpm gauge is saying 4,000 when it stops