Truck will not start on 2003 Ford Explorer Sport Trac

126,000 miles on truck. I shut it off 15 minuets later went to start it again and it would not start. Talk to a mechanic as I was out of town at the time, he said to try the reset button. I did this and it ran for a little over 100 miles and started stalling out on me. i had to hold the reset button down while my wife drove & we had to keep stopping every few miles until we got it home. I 've talked to a few mechanics they are telling me it could be the fuel pump went bad or even more likely then fuelpump relay switch might need replaced. I ma looking for some insight on this so I don't have to replace things that are not bad and spend alot of money unneccasarily.I also would like to know where I can locate the relay switch & if I should try to get a fuel pressure test done.

the reset you are talking about is for vehicle roll over or sudden impact from an accident to disable the fuel pump.
if you have to hold it down to run, then it is bad. most aftermarket places will carry this part.
a pressure test is a good idea ince you have other issues such as stalling.

My car did this last year around this time... I changed my fuel pump 3 times and my truck still would not start up... The whole time I just needed to replace the fuel pump relay switch... which was about 15-20 bucks? And my truck has been running find ever since!!