1990 Jeep Wrangler 1990 Wrangler 2.5 manual

Engine Mechanical problem
1990 Jeep Wrangler Four Wheel Drive Manual 80000 miles

My jeep drove fine, no problems. Started it up today and it ran for about 5 miles, then sputtered acted like it was choking and died. It did that all the way back to my home, where I put Heet in it and then I drove it again. For about the first 5 min it would run, act like it wasnt getting gas and sputter and try to die, if I gave it gas, it would be ok, but if I slowed down it would stop. After that it ran fine for about 20 min, no problems. I did this several times before changing the fuel filter which was god know how old. Took it for a test drive and it is doing the same thing. Its almost like if it runs for a bit its fine. Could it be fuel injectors or fuel pump? I can hear the fuel pump engaging when I put the accsessories on. Vacuum seal maybe? THank you for your help!