I also have a 1500 that died on me. It stalled on the highway after a few hours driving. My first thought was vapor lock but I have a new theory that might apply to you as well. Spark plugs.
Check what plugs you are using. When I changed my plugs a couple of weeks ago I went to my local supplier and asked for a new set of plugs. My book says that Champion N9Y was the original plugs. That translates to BP6E in the NKG brand. He asked me if I wanted BPR or actually BP plugs. I asked what the difference was and thats when he told me that the NGK "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking.
I then asked if it mattered which I used and he said that some older cars could actually stall from overheated ignition coil when using the newer "R" plugs. The symptom he described exactly what I experienced on a long highway drive last year and guess what spark plugs were in the engine! BPR6ES!
The engine would stall, just as if I had turned off the ignition, and then run fine again after a 15-30 minutes cooling. The engine itself was not overheated, temp was ok on gauge and the readiator fluid was nice and warm but not hot. I never really understood what the problem was and since I didn't go for any really long drives (and the Swedish weather is rarely really hot) I didn't experience the problem again. Now I guess I have to do some long driving to check that it doesn't happen again.
//Erik