Why is the truck stalling

Okay heres my problem.

I have a 1988 GMC C2500 Sierra, 350, 2wheel drive

On Wednesday while driving the truck was running fine one minute and stalled out on me the next. I tried to the point of draining the battery to get it started again and it just would not start. Went home and got a friend and another vehicle.

Once back at the truck my friend and I was finally able to get the truck started by holding the gas pedal to the floor. And once running. It ran fine.

Halfway home the truck stalled again. And again. Would not start!

Thinking that it wasn't getting enough spark, my friend and I replaced all the spark plugs right on the side of the road. After that it started right up. But again only by holding down the gas pedal to the floor.

But once started it ran good long enough to only get me within blocks of my home before stalling again.

Only this time I noticed that The cat convertor was beet red and damn near on fire. After that I simply gave up and had it hauled home.

Once I had the truck home, I went and bought a Brand New Muffler and Catalytic Convertor and put them on.I also changed the air filter and oil filter along with new oil.

When I tried to start it it started right up and took a moment or two before it began idling just fine. But once it got up to running temp it stalled again. I let it sit for about twenty minutes to cool down and started it again. It seems to start and run just fine and even sounds real nice. No misses or any odd ball noises.

But once it gets up to running temp the truck stalls. Let it cool and it starts right back up.

I am at my wits end and have no clue where to go from here. Any suggestions?

CAN ANYONE GIVE ME SOME POSITIVE FEEDBACK AND MAYBE A STARTING POINT THAT WOULD END MY TROUBLES?