Alright folks…

2004 139k miles on truck, ~42k miles on Atlantic British rebuild

she drives strong, but around 35mph, when the speed drops below or gets above I feel a jolt of sorts in the vehicle. Best I can figure with the timing and consistency that it is related to shifting gears (automatic btw). I feel the same around 50mph, though not as intense but still noticeable every time. There’s a slight clunk that accompanies this action, but no grinding noise or anything.

from what I have read it could be

- worn motor mounts
- Clogged trans filter (no clue if it was changed by any of the PO, but also no leaking or loss of fluid)
- front prop shaft going out (non greasable currently on the truck)
- bad fuel injectors (doesn’t seem likely but someone had similar symptoms and corrected it by installing new ones)

I’m hoping for any input here…my next step is a new transmission filter, then pulling the front prop shaft if the trans filter doesn’t help. Of course I’m willing to take advice from the experts if another plan of action may be in my best interest.

i’m about a 7 out of 10 on a mechanical level. Outsourced both head gaskets to a local rover shop, but prefer to save the hourly rate when I can do the work myself.

 

The front driveshaft is an easily serviceable item to cross off that list.
It doesn’t make sense as the culprit to me with your description - but it’s good insurance & known that it can be an expensive fail.

 

I have also heard that removing it, locking the cdl and driving it would help rule out if it is causing the problem

 

If the gears are shifting harshly then it may be low on fluid so you can check the transmission fluid level by running the vehicle until its at normal operating temperature and leave it running. Put on all your PPE, be careful and don't get burned during the following process! Make sure the vehicle is in park, chock the wheels and go under the vehicle; toward the front of the transmission oil pan there is a fill plug, remove it and see if a small stream of fluid comes out; if YES, its filled; if NO it needs fluid; add fluid until it starts streaming out.

 

I actually just drained/replaced the ATF about 1000 miles ago. Followed DiscoMikes directions that he shared in another thread.

was under the truck replacing o2 sensors today and figured I would double check the t fluid. Still streaming out when plug is removed at operating temp ~190 and having been driven about 10-15 minutes after o2 sensor install.

 

Was the truck running when you checked the fluid level?
At temperature is only part of the process. The engine has to be running and the autobox in park when you check it.

 

This sounds similar to exactly what I’m going through right now, mine was a distinct shimmy in the steering wheel. I took out the front driveshaft (super easy, at least with the driveshaft removal socket extension) and found a u joint bearing that was demolished. Like others have said, I took it out, locked the CDL and the problem went away.

 

Yes, it was running and in park