ok so basically here it is. Im sitting at a stop light, the light turns green, and when i push on the gas pedal, there is slack in the drive line that slaps to attention as i go. this only happen when i semi jump on it off the line. if i slowly ease into it, then the jolt doesnt occur. i know nothing about transmissions and select things about drivelines. my knowledge is all in suspension. also, when the truck is in park, i can rotate the drive shaft back and forth a bit. do you guys have any ideas as to what it is? the truck has 100,000 miles on it and the person who owned it before me towed a trailer with it. do you think its the u-joints, gears, transmission?

 

Mine has a little bit of play also. I was worried about it until i tried my dads Cummins and his was a little worse then mine. I'm not sure if it's a bad thing or not?

 

I would check your tranny mount, my camaro would tear the stock ones in half and back the screw off the performance ones.
there is a bolt going through the mount, make sure its tight, and the mount looks good(no tears)

 

check the driveshaft slip yoke.I think thats what its called.Had mine greased and it stopped for a few months but is now back.I believe i heard something about a nickel plated yoke that fixes the problem

 

Nickle Plated Slip Yoke FTMFW

 

so with the slip yoke is it just spinning freely or moving back and forth? i dont get it

 

me either. i was thinking it might be the gears in the rear end because they have 130,000 miles on them.