i have a '94 chevy pickup with a 350 tbi. a new distributor was installed a year ago and timing was set. now we had it in again and the timing was 6 degrees off. what could be the cause of it? the motor has 170,000 miles on it and its been worked too. its a farm truck so were always pulling loads of cattle with it and it gets stopped and started basically all day when my dad goes from place to place. any help would be great!

At 170k..timing chain slop first and secondly..a cam helical gear chewing up the new distributor gear.Pull the dizzy and inspect the gear.If it shows a normal wear pattern..reinstall it and jiggle the crank back and forth while observing the rotor tip.At 170k..I would just spend the few $,s and put a new chain and gears in it.