k1500 cheyenne "Big Red"

Hey yall so my baby a 1995 k1500 Cheyenne edition "big red" has a problem with her so I was driving her bout a weak ago now and it felt like she was losing power I would shift from 2nd to 3rd at 30mph 3k rpm and I would lose all power, the same thing happened in 2nd and 1st until eventually it would just stop and I wouldn't be able to move it unless I revved it up to about 7k rpm and pulled the clutch real slow. So I pulled off and realized my thermostat was shot, I replaced that and it happened again. Anybody else had this problem or know what might be wrong?