Lumina Engine Problems/ Running Lean

I got a 96 Lumina LS and I have been coming to this site to help me fix all my problems, but now my car is doing something that i can't find on here or it might sound like something but wasn't sure if it is.

The car started to go down hill when the tranny went out in it.. Took it to a drunkin mech(My First Mistake) and had him put the tranny in. Well the bone head never hook up the, I believed its called the TCM and didn't put a filter in it. Well got that all fix and still the tranny is givin me problems. For some reason when you first start to drive from a cold start it would shift fine and do the gears like its suppose to.. But after it warms up or I get on the gas, overdrive or something would not kick in or it kicked but its not running right.. at 60mph the rpms are @2300 - 2500 and i know that ain't right.. Thats the first problem.

The second just happen to me a couple of weeks ago, I just did a normal tune up right.. (spark plugs and fuel/air filters). The wires are brand new with no more then maybe 5000 miles on them.. and there ACDelcos. Well the plugs i put in are Bosch and the fuel filter is a fram... well after i did all this.. The car went nuts as in, as soon as it would start the car would chug and then die, or when i try to give it gas it would die out.. or sometimes it also when i try to give it a lil gas.. it would try to die out then rez up to 3000 rpms and like get stuck there for a couple of secs..

The plugs that i got where gap wrong so I gap them to the book spec 0.60. and the car has 213,000. What should I do?

And I got some Codes to if this helps.

History DTC P0171
System Too Lean
(Bank 1)

History DTC P0300
Random/Multiple
Cylinder
Misfire Detected

History DTC P1870
Transmission Comp
Slipping.

First of all you should have used AC oe type plugs, Bosch will not work in these engines, second sounds like a bad plug or wire causing the misfire, recheck all the plug connections especially in the boots at the plugs. 1870 is a problem with the trans controls or internal slippage, this must be checked using a trans function scanner in the hands of a trans tech. Also check fuel pressure here and look for any vacuum leaks or air getting in behind the maf ducting.