I have a 94 gmc 1500 and a few weeks ago I started having issues with it starting. One day it would start fine and the next day it wouldn't. I changed the fuel filter thinking this was the issue. The truck did fine for a week. The other day it wouldn't start again. Cranks really strong but just wouldn't start. Set for two days then went to start it and it started on the first crank. The fuel pump is running when the key is turned on. Any ideas?