[A26B]

Originally Posted by onetinsoldier

Ok why is it that shifting into 6th at 65mph , makes everything shake like its coming apart ? It kinda clears up around 80mph ,is it low rpm's due to 2;73 rear gears ? Not going fast enough for proper gear meshing ? ok open for answers !

OK, given that you have now confirmed 3.73 gears in a follow-up post, there is no question that you should be able to accelerate smoothly from 65mph in 6th gear.

NOT a gear meshing issue.

I suspect a spark problem.
May be be coils or wires.

Check spark;
Suggest you use a spare spark plug to test with. Best done in dim light
Engine off remove one plug wire
Insert spare plug in plug boot.
Ground plug
Start engine
Gradually increase distance of plug from ground & observe spark color & length.

Good spark is blue in color & will jump 1/2"~3/4"
Weak spark is orange in color & will not jump far from ground
Bad spark is obvious

If you have weak spark, note the cylinder number.

Repeat for all 8 cylinders

I'm not an advocate of measuring resistance of paired cylinder plug wires & the coil all together. It serves no real purpose since the plenum has to come off for either wires or coil. With the plenum removed, you can ohm the plug wires individually and check the coil independently for meaningful results.

If all 8 cylinders have good spark, then your problem is most likely fuel injector related.