Truck Repair: 88 Chevy Pick-Up, throttle position sensor, vacuum leaks

Question
I have an 88' Pick-Up(4x4 350). I have had this problem that when I am driving and I give it some gas, it will act like it is about to die but it hasn't yet. But, if the "Service Engine" light comes on, the truck will run fine. It's like it is in a safe mode or something.  

Answer
That's called the limp-in mode.
I would first check the EGR valve to see if it is seating on some carbon, which will act like a big vacuum leak.
Look for any other vacuum leaks also.

Next, depending on the equipment you have, I would test the fuel pressure...13PSI when running. Possibly replace the fuel filter.

After that test, test the throttle position sensor, for smooth consistent sweeps throughout the range of its travel. Ohm meter, or a scan tool.

Van