So I got this truck used with a jasper motor and a rebuilt trans and when I got it I was told it had around 1,000 miles so right now if I start from a stop and hammer down WOT there's no 1-2 shift the motor goes to 3-4000 rpm and starts to act like its on the limiter and falls right on its face. Now if I'm going any faster and get it to down shift at wot to 2nd it will do the same thing I have to back off for it to shift and when it does it's only at about 1500 rpm. Today it will get to 3k rpm and do the same thing(act like its on the rev limiter) I've changed the fluid and filter and the tps and the fuel filter. I scanned it and the only codes are for O2 sensors. Fluid is all under my truck though, looks like it's coming from the vent and at the bottom of the bell housing.
Any help would be great

1997 Chevy k1500 5.7 4l60e 4x4

 

Also I put it on a snap on scanner and while I was in park at idle it said the trans was in 4th gear but all other positions other then 1st read what they were supposed to be. While in first it said it was in 2nd. But the trans does shift through all gears. If I manually shift it, in l1 it still shifts 2nd around 3500.??? I was told it will do that due to a safety switch but I'm not sure if it's gonna do it at 3500rpm. If any one could tell me how I can read the pressure in my trans and if anyone knows what trans data bank 2 is supposed to look like in the scanner would be great.