Hi,

My 2011 Silverado has 155k on it, has the 5.3 Vortec in it.

It seems to rumble a few seconds during idle then returns to normal, then does the same. Seems to be on repeat.

Its shifts very very hard, no real slippage, does go into gear. Performance is down slightly, so it seems. Rides great on highway speeds. But has the issues at low gear. Shifts hard from 1-2 to 3. No odd noises, no whines, no clanks, no clunks, quacks, or ***** (haha). Does not seems to have the classic transmission shudder at all.

Tried the Lucas fuel injector cleaner, big bottle, no luck. No codes at all. TPS read it was at 17% throttle or so at idle. Reads about 24% when at 2.5-3k RPM. Normal? Not sure.

Has fresh tranny fluid, fluid looks good. Fresh oil change.

Fresh spark plugs all around.

Fuel pressure is at 42-43 PSI at idle.

Please help. Im racking my brain hard. Super nervous that it needs a transmission!

Any ideas?!?!?!?!