1996 g20 codes

[Warped]

Well i just bought this g20 a couple days ago and after driving for about 100 miles the check engine light came on

1.0304 - knock sensor2.1103 - improper shifting to 1st gear position3.1106 - improper shifting to 4th gear position or tcc

a little backround , the auto transmission slips. 1st gear doesnt slip and either does second .When second is shifting into 3rd it takes and bit and feels like its slipping pretty bad.in 3rd gearits slipps pretty bad but when i get on the gas it kinda grabbs and gets me up to speed. and OD[4th] slipps all the time cant really even keep the car moving when it shifts to 4th.but it does shift to 4th so i do believe the TC is locking up but cannot be for sure.I've read through the FSM for my car and found out how to check the knock sensor but didn't really find alot about the trans.I went to the local u-pull it yard and pulled an auto trans from another 96 g20 with 130k on it.Trans fluid looked good and didn't smell burnt at all .With your guys knowledge and exp to the transmission codes mean 1.the trans is toast?or just bands?2. should i replace the TC also or just reuse the one in my car now?(im pulling the pan this week and replacing the filter and gasket and going to see if its still slipping and if there is crap in the pan)any help is appreciated thanks