well it is no big thing but i am pretty sure that it is not meant to be like this .

when i am going down the road in drive it is fine during acceleration but as soon as i let off the gas it will kind of make a klunk noise and will start to decelerate fast .i believe this to be coming from the transmission and it is mostly noticeable around 30-45


any clues??? ive lived with it for this long it is not like it is hurting any thing

(btw the atf is up to level a little dirty but i plan on changin that soon the u jointas are all new and good and the diff lube is bran new and up to level)

 

This may sound way out there, but these trucks are famous for the parking brake cables sticking. I would take it for a little drive, and then see how hot the rear brake drums are.

If that doesn't look like the cause, change the fluid and filter like you mentioned, and take the flywheel inspection cover off and look for a drain on the torque convertor. This will get all the fluid out. And while you are under there, spend a little quality time, checking things over, tightening bolts, checking for oil soaked motor mounts that may be bad, broken rear leaf springs, rusted out u-bolt mounts, etc.

 

HERE'S ANOTHER OUT-THERE IDEA. IT COULD BE THE HEAT RISER THAT'S CONECTED TO YOUR DRIVER'S SIDE ESHAUST MANIFOLD. IT LOOKS LIKE A SQUISHED TIN CAN WITH AN ARM STICKING OUT. WELL, THERE'S A LITTLE CHOKE PLATE IN THERE AND IF IT GETS STUCK ONE WAY OR ANOTHER IT CAN CAUSE A POPPING NOISE TO COME FROM UNDER THE FLOOR BOARDS DURING DECELERATION. IT ALSO CAUSES THE EXHAUST TO BE CLICKY SOUNDING, LIKE A LOOSE ROD. CHECK TO SEE IF THERE'S ANY LEAKAGE AROUND IT OR DAMAGE. IT COULD>>> BE THE u-joints BUT I DOUBT IT. BUT IF ALL ELSE FAILS, RESORT BACK TO EITHER THE CONVERTER OR TRANNY FLUID.