530d won't rev above 3500 rpm

Clean MAF and Throttle Body.

how to stop a Chevy Tahoe from misfiring and smelling gas

STOP doing that, forget about it, your going to blow your engine !

You have a misfire, so you don't need someone to
tell you to diagnose what you already know you have

It won't rev past 4,000 rpm, because it is programmed that way,
just so you don't & ruin the engine

If you want to play--- get a car from the 1960's & have some fun

Due for a transaxle rebuild,common on that veh

The fact you continued to drive it when it won't
shift correctly & has been slipping, your done

Check your distributor bearing. I had a car that had the same problem. It was the distributor bearing, it didn't allow the distributor to advance.

Just a thought....

sounds like its time for a tune-up...

Sounds like a torque converter internal problem or the pump is bypassing fluid or there is air in the torque converter. Hope this helps.

on almost all gm cars after 96 the engines were governed to not free rev over 4000rpm. when in gear and power braking the rpms stay lower cause of the load on engine. when reving above 3500 rpms the computer cuts back the timing and fuel to reduce engine damage if left to free rev. hop that helps.

Try the Transmission fluid. If the level is low then the hydraulic vacuum type operation is ineffective