i have a 1988 gmc sierra 1500 and if you put it in drive and put your foot on the gas pedal it barely goes

as in the before said it barely goes then eventually gets up to speed i know that someone advanced the timing to about 14 degrees when i put it to 0 degrees and put it in drive and stopped to get out on the street it lugged and then died so in order to keep it running it has to stay advanced the tranny was rebuilt not to long ago and the truck has done this ever since we have had it and has only gotting worse if you start at the bottom of a hill in park in will not go up the hill we have changed the vaccuum advance cleaned the carb plugs wires cap rotor i think it lugs at the begining of ever gear please help i think it is driving me a little nuts or bolts whichever you prefer thanks