rpms surge

i have a 99 blazer 4x4. the other day the rpms started to surge 200 to 300rpms while driving around 50mph. it also sometimes happens at other speed. it will only happen after driving for about 20 min. i was able to get a scanner and found that the tcc was engaging and disengaging. the pulse width would change as the rpms surged. it seems like something is commanding the tcc to turn off, but i have no clue what could cause that to happen. any help would be greatly appreciated.

it may be a coincidence but it seemed to act up more when i had the floor heat on and after turning the heat off the problem seemed to go away

Have you got another post on it hear anyplace?