97 GMC Sierra 1500 Stuck in 3rd Gear w/ no codes

[CasperDC]

I have a 97 GMC Sierra SLE 1500. The truck is stuck in 3rd gear according to a code reader and will not shift up or down. I have changed the tranny and all the fluids numerous times. I have tried resetting the codes with the code reader. I have tried resetting them with disconnecting the battery cables. I have also tried changing the fuses, but still the truck will not come out of 3rd gear. I am not sure what to do now. I have also changed most the solenoids on the tranny. Just got the truck and haven't got to go out and play in it. Any suggestions? I can't just take it to a shop when I live an hour from the closest one. I have also changed the ignition switch. When I changed the ignition switch is when the codes stopped but the truck is still not shifting and still acting the same as before but with no codes. It gets to about 25 to 30 mph then high revs to 4500 to 5500 rpms and acts like it's in neutral and will not shift.

Please some feedback needed. I'm really frustrated and confused.

Thanks