1994 olds bravada possible bad transmission

When i'm driving i have no power in Overdrive, i have to drive the vehicle in Drive, 1st or 2nd. If i step on the gas it feels like the transmission is slipping, no power. When im going up hill i have to down shift in order to make it. Also there is a slight humming noise coming from the transmission/transfer case area. The humming starts out very quiet as i accelerate it gets louder until the transmission shifts, then the humming gets very quiet and once more gets louder as the RPM's increase.
am i looking at a transmission overhaul? a transfer case overhaul?

Welcome to AF, tough to tell what is wrong by your description this really should be road tested by a tech for a proper diagnosis.

I guess you're right.
i'll try to elaborate a little more.
i don't think its the fuel, i recently replaced the fuel pump and spider injector, now i'm getting 61 psi. I also changed the O.2 sensor.
the truck runs fine. About a year ago i lost the 1-2 shift solenoid, so while i had the pan off i changed both shift solenoids, everthing looked nice and clean. No shavings or junk in the transmission. I ran it to Jiffy Loob and had them do the flush treatment just in case, does a '94 use a special fluid other than dexron/mercon III? If i stomp on the gas, rather than shift into overdrive or give me that boost of power it bogs down, i have to feather the gas pedal in order to increase speed otherwise it just slips.

if this doesn't help i guess you're right i'll have to run it to a tranny shop.