I have a plow truck, 87 f250 truck always ran great... I always usually fix everything myself but this had me wondering - So i braught it to the local mechanic - trucks not in front of me dont remember if its a 302 - or 351

it been doing this for 2 year's -- every time gets closer in duration it seems -- Here is what it does - when it act's up ..it almost always on initiall startup.... start it ...runs high idel's down then runs almost instantly super rich... To the point where gas is coming out the exhaust.. buck's barely runs and isnt what i would consider driveable on the road... then sometimes clears up on its own , OR pulled of a vaccum line in the back or sprayed pb blaster in the little vaccum thing and it would clear before i had to change all the oil before it got filled with gas...

Braught it to the mechanic and they changed fueal pressure regulator..{my idea} should have done it myself ... then in tank pump... and he's giving up because its a plow truck and doesnt want to see me spend any more money... im leaning towards something mechanical rather than electrical.. because of the vacuum disconnect and it running fine? ANY ideas would be very helpfull!! this thing has been at the shop for over 2 months and now has me strapped for time...