1992 Pontiac Transport stalls

I have a 1992 Pontiac Transport with the 3.8 and 86k. It has been doing this problem for about two years and has everyone stumped. Durring the winter months it runs fine with no problems. After it turns 80deg or warmer in the summer it starts its fun. With out warning it won't start, once you first turn the key and find the no start you can count the seconds to 30 minutes then it will start and run fine. It might happen twice in a day or only once a month. Never in the colder winter months and never first thing in the morning. Only code is a locked up torque converter. After it starts is runs fine down the highway or in city. Other problem, again only durring the summer months and usualy on only hot days. Driving down the highway it wall sputter and stall. Wait a few minutes and it will start and maybe run 1 mile or two days before it does this. All these problems have been intermettent until this summer, now they seem to be happening a little more frequent.