98 Pontiac gtp shifting problems

I have a 98 Pontiac gtp shifts good from first to second at about 15 mph but will not shift into third until I get speed up to 50mph and a high rpm shifts into all other gears after third at normal rpm and speed why does it not want to shift Into third correctly?????

Scanned for Transmission codes?

Put the car in manual first and drive.....then manually shift into second......then manually into third......

Did you "feel" the normal 1-2 and 2-3 shift?

It's normal from first to second the only problem is shifting into third it shifts perfect in every other gear I scanned the tranny shift silonoied A and something about TCC FAULT or something I'm not around where I have it wrote down

And yes I tried shifting manually it does the same thing

I am having the same issue with my 2001 GTP. One thing that I noticed is that while I am driving it the mph gage seems to work but as soon as I take my foot off the gas the mph gage drops down 0 mph even though I know I am driving faster than 5 mph. Does anyone know what this might be indicative of? Also the car seems to not slip as much when I am giving it more gas from the get go. If I slowly try to go from 1st, 2nd, 3rd, gear etc it seems to have a hard time getting to 3rd. Zep