Chevrolet Repair: 1998 Chevrolet Tahoe engine knock, grasping at straws, chevrolet tahoe

Question
Hi, once again, this jerk happens only when moving. The weird thing is that the car is working
perfectly fine when driving in the city, But when i get to the freeway and move with speed
somewhere about 60-80 km/h, rpm 1500 there is knock coming out of the middle of the car.
The car is moving on the freeway, without load, so I accelarate gently not to lose the speed and
then  let my foot of the gas pedal for a moment. The knock is not periodic, it's single. It can only
repeat after awhile, but there is no particular cicle. So this knock happens only while moving, I've
cheched my AT two days ago and it was perfect.
Thanx for any help
? Followup To
Question -
I have 1998 Chevrolet tahoe and it has a light engine knock or
ping, feels as if someone is trying to stop the car from behind,
at 1500-2000 RPM, normal cruising speed. It sounds like some
sort of a hit. Ran a snap-on scanner on it, got no codes and also
checked while i was driving,
operation of the knock sensor, it would show a maximum retard
of 4 degrees when the truck is a full throttle and anywhere from
1-2 degrees at cruising speed. Ignition timing is at 28 degrees
cruising with no load and dips to 17-18 under heavy load.
Voltage for sensor is 4.75. So right now I'm not sure what to do
and everything else seems fine."
Answer -
Hello Artem,
I am curious about this "stop car from behind".
Does that mean you can kinda feel it slightly jerk?
Does it only happen when moving? What happens if you hold it down one gear, and drive at the
same RPM's? I am wondering if it is RPM related. or Speed related.
It may not be the engine, in other words. A fear axle bearing trying to lock could make a similar
jerk from behind.

But don't let that guess from me scare you. I am just grasping at straws. You are the one that
needs to see if the bump, etc is engine related or whatever. I can only go by what you mention.

A detonation inside the exhaust system could also feel like a bump.

Van

Answer
Hi Artem,
If the knock is just when you are releasing the torque, is it possible that the slip yoke in the driveshaft is jerking as it moves on the splines?
During acceleration, the rear end tries to come foreward, thus shortening the driveshaft, but if the splines are worn, they will resist sliding in while torque is most, but as torque lessens, the side friction in the splines releases, and allows the slip yoke to slip.
I have heard of replacing the orriginal slip yoke with a nickel plated one that is supposed to last much longer.
See if by slowing down, then accelerating, then slowly letting up on the gas is when it does it.

Van