Im at a loss here. Have a 91 3.1 when cold cranks and fires right up and runs good. When hot cranks fires then dies immediately. Any have or had this issue? Where/what to look into? Someone help me out please.

 

I haven't had this kind of a thing on a car, but I have run into similar stuff on motorcycles.

Old electronics can work fine when cold, but when it heats up, a small crack somewhere can expand and make something lose contact and fail.

The best thing would be to have a shop scanner that can read live data (most cheapo scanners only read codes). A higher-end scanner can see if there is a sensor not sending a signal when hot. Like, say, you have a bad crank position sensor. Ignition coils can have this kind of failure too, but you have three coils, and one failing won't immediately stall the engine. And all three failing at once in the same way is really unlikely.