The 7K engine speed only matters if it's in drive/3rd gear. All other gears the driveline speed it significantly reduced.
https://spicerparts.com/calculators/...rpm-calculator
At 7000rpm and 1:1 transmission ratio the truck speed would be 135mph.
I am no expert, however a two piece drive shaft would be supported in the middle and as such would have a reduced tendency to whip at the first critical speed.
It could be a lower cost solution? You may have enough power to run a higher differential gear ratio?