Couple of concerns

[JamesV]

Straight to the point. 2008 with 249k on it 4.0

1. Every now and then i get a shake while driving, sometimes before a shift. I wouldnt say a rumble strip but more like a scared dog. No delays in shifting or slipping, done in a nice smooth manner. Tested torque converter lockup at 55mph with no issues.


2. At cold startup I have a knocking sound from the front of the vehicle but unable to isolated. Best way i can describe it is it sounds like someone hammering something in the room next to you. No issues with misfires or codes at this time

 

[RobStoration]

If your shutter is between 20 and 30 mph at light throttle then it's probably transmission slippage. Take a look at the color of your transmission fluid.

For the knocking at cold start, it could be a very light piston slap.

 

[Moist]

I have a mild shudder from 55-80. Mine is due to a knackered steering rack that I cannot fix for the time being. (popped seals with a PS leak from inner tie rod ends)
Jack the front and up and test for play. There will probably be a little for the steering system but generally its fine so long as the play it makes it up to the steering wheel. Depending on what you see there it can make or break a lot of ideas on what's shaking. (if there is play which directions? Does the steering wheel move? Is there a knocking or clunking sound?)

Otherwise get on the brakes when it starts shuddering, if it gets significantly worse it is most likely a stuck/seized caliper or a rotor that has excess deposits or is warped. (I've had 2 seize in a partially closed position before and they force a strong vibration while driving. Sometimes you can hear it as a squealing or the brakes ticking and popping after a long drive.)
There is the possibility it could be other things too like a bad driveshaft or something buggered with the transmission but I don't know how to diagnose those.

Also how are your manifolds? Mine are broken and sound like a bottom end knock or a thumping behind the dash. I thought my engine was dying and it turned out I have several rust holes in mine