[Bassasasin]

Welcome to the Forum. your engine type when no bugs in it will run 200k+ miles. Hang on

First your posting several problems on one thread.. not to your advantage or ours. Perhaps a moderator can straighten that up.
But anyway,

Is yours supercharged?
Is it cold when you try accelerating?
Many sensors control the mix at different times. MAF, IAT, ECT, O2.

PERFORMANCE PROBLEM
I suspect you only have one problem causing several symptoms here. I have heard of new aftermarket Crankshaft sensors acting up.
The new sensor may have come loose or clearance mis alligned..
The Tach acting up may be sign of the ECM not seeing the RPM properly, as you may have guessed. However usually the engine will suffer or surge with the drop if its the Crank sensor, unless its a wire after the ICM Igition module going to the ECM computer, then there would be less noticable RPM drop. The ECM may do some adjusting for what it wrongfully sees.

Servicing the transmission will usually get you a new pan gasket and change fluids.. Quite often just a fluid change will help those little valves work better and has cleared shifting problems. Probbly an advantage to you if the transmission has 80k miles.

If it continues to throw a new code after cleared you may think of put it through a diagnosis shop. $$ It may be the signal to the ECM from the ICM thats messin up. In my model the sensor transmits to the ICM, the ICM cable comes from the ICM goes to a connector under the Alternator and then to the firewall connector and then to the ECM. Any of which could be intermittent.. Popular problems noted by GM are at the ICM connector getting dirty and I believe they are addressing that on newer models.

NOTES
I understand the shifting is controlled by the ECM via sensors. (duh?)
Learned this by seeing ECM performance chips CUSTOM EPROMS can change the speed at which the transmission shifts.

WINDOW
You will have to check the wiring for source voltage comming into the door. Voltmeter and tracing. Opening door panel and such. There is a connector problem in forum mention to fail just inside the door as it goes in near the hinge causing your symptoms. If you tackle this you may ask the forum for color codes and be ready with a DVM volt meter.

Perhaps a little more info may help forum participants and can give you more focused direction as your next step.

There are extreme experts here as moderators and participants.
There are also shade tree mechanics.
Watch for Moderator responses..

RECHECK CODES.

Welcome and Good Luck