OldIHC

Ratios for stock 4'spds (either of two) is 6.4, 3.09, 1.69, and 1:1. Since I already had my K manual out

I installed a dana 70 rear in it. Reading numbers off the ring, its 41 11, 41 tooth ring 11 tooth pinion. 3.73. So where's that put us?

4 speeds are still 1.00-1 in fourth gear, Now you say you swapped rear axle,,,,,,,maybe saved some time to disclose that first post?

not fast enough, gearvendor overdrive,

I said it was a 3.73. Nobody wanted to believe. I just cant see how 1to1 and 3.73 will top out at 40. Got to be something else.

Well, because you didn't disclose the swap, and the fact that stock ratio's are roughly double that, and your saying that it topped out at 40, every one naturally assumed that you mis read the rear ratio. Don't be upset at us for your leaving out key facts.
Since I doubt you are still running stock 20" rubber on that Dane 70, what tires are you running, what is their Rev/mile?
Don't make us guess what you have!
Depending on rubber, that 90 hp GRD may not have the power to move it faster with the tires and gears you have.
Why not tell us exactly what the running gear is?

Based on what you've disclosed so far, possibilities are:

driving in 3rd instead of 4th,

running really small wheels/tires,

inaccurate speedometer reading from not compensating speedo drive after swapped out axle,
(drive by a radar sign or use GPS to verify)

mistaken on actual rear axle ratio, (verify axle ratio)

take your pick

or depending on what else you haven't shared could be anything,

Oh, and as CB said, If you are doing all this with a GRD 233, it isn't up to pushing at that ratio, you may have ratio you need, but motor doesn't have the poop for it,