Running rough. At 70-75 km/hr it seems to

use a couple of quality injector cleaner in the tank
run fault codes
remove and clean injectors
check fuel pressure

if the shaking is coming from the rear end, have you checked the tires to make sure you havent broken a tredd in the tire and make sure the tires are balanced correctly and one hasent lost a wheel weight and thrown it out of balance. and check the air pressure in them also. check all tires i hope this helps

tires out of balance or showing threads

change trans fluid and filter and a fuel filter might not hert

well if the truck feels like it is shaking under you its got to be a tire with a broken belt, or if it is shaking on the steering wheel its something in the fron end

check the spark plug gaps. [I think it should be 0.8mm ] too small or too large - for surging [ incomplete combustion ] . rough belts- squeel ? check correct tention & spray some penetrating fluid like CRC on the pulleys . But for the **** I really dont know what to suggest

CHECK THE BALANCE ON TIRES AND CHECK FOR A BROKEN BELT IN A TIRE. I WOULD ROTATE TIRES TO SEE IF THE SHAKING CHANGES ARE EVEN GOES AWAY

Sounds as if your brake rotors are warped from overheating. You can have them machined to take this out if they are thick enough. This should take care of the problem, if not replace rotors.

hesitation not getting power shaking while idling and service engine light flashing and sound like muffler bad

HAVE THE TIRES BALANCED AND CHECKED FOR SEPARATION