1999 Envoy vapor lock/air cond cut off

I have experimented with vapor locking episodes on my 1999 Envoy. Last year it did it several times. At first I wasn't sure that fuel injection engines vapor lock, so it took awhile to realize that it was a vapor lock. It always starts fine when engine is not hot. It also has plenty of power. Last year normal vapor lock issue would be when the engine was turned off for a couple of minutes on a hot day. It would not restart for about 1 hour until it cooled sufficiently. It also would quit running on the interstate on 90+ days. Let set for an hour and it would start, then run several miles and quit again. I had a coolant leak and finally found it. I had a couple years ago installed a 195 degree thermostat. I was getting very high temperatures (210) at times in hot weather and long driving conditions. I found out that the radiator was plugged. Ended up replacing the radiator. I also installed a 180 degree thermostat. I thought it should fix the problem as the temperature gauge shows much lower. But experienced the problem again a few days ago. I am now going to insulate the fuel lines and try that. But my air conditioner also cuts out in hot weather. The compressor doesn't engage and would typically cut out right before it vapor locked. It has refrigerant. Is there any type of high temp switch or anyway that these items are related?

These problems are probably not related, and I highly doubt it is vapor lock. I would be money your fuel pump itself is failing. You need to perform a proper fuel pressure test. The key on/engine off pressure must be over 60PSI. These trucks demand near perfect fuel pressure all the time.

As for the A/C, again, I highly doubt this is a heat issue. You need to find a good A/C tech that can troubleshoot and fix it properly.

I agree b1lk1, it is likely not vapor lock. If you have a vapor lock issue, you have leaky injector(s), but thats most likely not your case, and vapor lock will not cut it our on the highway. You either have a fuel related issue, or ignition issue, something like a crankshaft position sensor, etc. When the truck dies, thats when you have to be checking things out. I would start with the fuel pressure, like mentioned. You need a guage to see what it is at that point. If the pressure checks out, then you need to check for a good spark.