i searched and posted in here about a problem with the truck not getting any spark when its cold out in the winter months i have found corroded wires fixed all i seen with no luck but as soon as it got warmer the truck started fine no problems what so ever with the spark issue, then it jumped all over the place like you was hitting the gas then brake, gas, brake, and so on changed the fuel filter gas in it was black as coal. no more jumping around it just bogs down like its running out of gas, but it doesnt do it all he time some days it runs great for awhile then it acts up there is plenty of fuel in it. the motor has been changed prior to me getting it, and i think it may be out of a 90 dakota not to sure it has a voltage regulator which i was told wasnt supposed to be on it and it sometimes stalls out when u slow down to make a turn or come to a stop, it is showing codes 12, 41 ,21 so far. any input would be greatly appreciated

Have you changed the fuel pump ?

no i thought if it was bad it wouldnt run, but it turns on when u turn the key on. i dont kniow if the guy that had it before changed it.