Trans doesn't seem to wanna downshift
 

I recently bought a 98 T/A , this is my first LS1 car , previous cars ere a LT1 Corvette & 95 T/A. The trans doesn't seem to wanna downshift over 30 mph . I'll floor it , but it just seems to keep going in the same gear. This was an Ebay car and I didn't get to drive it until it showed up on my doorstep. It is a bit hacked together . The guy had a built motor/trans in the car and sold that and put a stock motor/trans back in . The engine light is on for the rear O2 sensors because the car has headers, no cat , borla cat back . I don't think the rear O2's would have anything to do with the trans shifting . Also , theres a harness that was cut up under the center console , it had green & white wires going to it . You can also shift the car into any gear without having the key in the ignition. Trans fluid is at normal level and doesn't smell burnt. Anything I can look at that would affect the downshifting ?

TPS ?
Johnny

Stock tune doesn't want to downshift below 38MPH
(3.23 car) except at TPS >96%

Have seen several cars which couldn't hit TPS > 90%
due to pedal / cable slop.

Stock tune sucks, factory slop can make it worse.

Replaced the TPS, its not that . Is the stock trans really this crappy ?