1997 Gmc Jimmy Transmission problem

I have a 97 Jimmy 4X4 with a 4.3, auto trans and push button trasfer
case. It has 130K miles and is not modified or driven off-road. When
accellerating from a stop it seems to stay in first gear until I
release the pedal , then it seems to shift to third and works well in
third and overdrive (converter locks up in drive and overdrive).It
will stay in first while rpm reaches 4000-5000 and not shift until rpm
drops below 2500 with low load. If I try to accellerate on the highway
(say 55mph) the converter unlocks, then the transmission shifts to
third, but if I force a shift to second the engine will race and the
truck feels as if it is in neutral range (no longer "pulling").
Any thoughts? Thanks to all!