'99 Venture Stalls in Reverse

[GJR7318]

Hi,

So I recently bought a used chevy venture. Car seemed to run fine, but then started to run hard all of a sudden. Took it to my mechanic and he fixed the intake gasket which was causing it to leak coolant into the oil (I saw yellow slime on the inside of the oil cap). This has been fixed, changed oil, filled coolant. My car now proceeds to stall out once in a while but only when I put it into reverse. No idea why. Along with that it started to begin to overheat. I let off the accelerator and it cooled off. I had the heat on about mid-way and it was blowing hot air, when I turned the heat off the temperature gauge seemed to stabilize at a normal cool temperature. Any ideas? Thanks.