84 Diesel Pup Problems--Please help

Hi, After a long, cold winter, my Isuzu Diesel pickup starts and idles just fine, but after it warms up and I try to take it for a spin, it bogs down. It won't go over about 10mph and stalls after throttling.
But it will start up again, move a little further, before dying again. I've checked for air intake blockage (none), water in the fuel filter (none). Any ideas on what might be the problem? Thanks. Josh
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