trany prob on 99 escalade

i have a 99 escalade and my problem is when i floor the gas the truck revs but it wont shift out of the gear and feels like the truck is strapped down and doesnt want to go. i let off the gas a little them press again and it lets the trany shift then all is normal. any help would be appreciated. thanks

Could be:
Low fluid level?
Sticking kick down cable?
Sticking modulator?
Vacuum leak causing modulator not to actuate?
Worn spool valve?
All easy and quick. Good luck.

... or it might be a GM 4L65E and its destined to blow :) Check all the external stuff like Public said, but if that doesn't do it you might be looking at a full rebuild. Those of us with the 4L60E (your tranny's predecessor) sometimes get as little as 36,000 miles out of ours. Mine is failing miserably at 86,000. Some of use upgrade to the 4L65E guts to get some more life out of them, but they are not long-haul trannys.