Need Help with transmission in my '93 GMC
 

I have a 1993 GMC 150, Two wheel Drive. 4L60E Transmission.
Had the transmission rebuilt about 3,000 miles ago. Since then, while driving in overdrive (D2), it seems as it starts reving up and going in and out of gear, it works pretty good most of the time in the gears but it kicks in and out of overdrive. It runs good in 3rd gear... The guy who did the rebuild moved and cannot be located now. ??
Any suggestions ?? Thankis Lou Conkey 3850 Stock