transmission problem

i have a 1998 chevy silverado 4X4 with a transmission problem. the frist and second gear are fine, but then it goes into nuetral and wont shift up. the fluids are all fine. i heard somehting about a 3 and 4 clutch pack. anything would help. thanks

I would have it scanned for solenoid and internal slippage errors, but it most likely will have to come out and apart..Possible the main connector is loose, some issues with ign switches, but there would be ancillary problems with this.