Why is engine stalling?

Thanks in advance to anyone that can give me some 411 on this. Car is a typical 440 `71 Duster implant. `74 low comp externally balanced engine w/ stock cam, stock heads, Holley 750 Dominator 2X pumper, Weiand high-rise intake mnfld, ProParts headers, MSD, 727 RMVB, 8 3/4 rear w/ 3:55 posi, 29 in. M/T ET Streets. New heads or port job and hotter cam to match setup in the future.....Converter the next thing on my list however; low stall factory unit (ballanced) in it now. Probably going w/ B&M Holeshot 2500-3000 unit w/ B&M flexplate to balance it, 3:91 gears too (opinions?). Mostly a cruiser but may head to Epping someday when engine mods are done. Problem is that the car will stall coming off the highway at the bottom of the off ramp. Highway cruising RPM 2500 @ 60 MPH. When this happens the engine struggles to turn over and restart. Unburned fuel in the cylinders causing the tough turnover? No problems w/ starter motor/ turnover/ startup any other time. Also a stalling problem in 1st at stoplight when the temp is below 180 or 190 degrees. Is the tight converter the problem or the mix? Or? Engine does need total tune for sure.....