Mr. Higgins,
Respectfully, why do you need a trans with an overdrive? In M1009 trim, they do just fine on the highway and interstate going 70 plus mph. The M1009's have 3.08 gears. The rest of the CUCV crowd likes to upgrade because we have 4.56 gears as supplied and running 55 mph down the road sounds like an early death to the engine. Ok, Rant Over and somewhat rationale thought applied.
My Wife has an 09 Tahoe with a 6L80 trans mated to a 5.3L engine. At 55 mph, it is only turning 1,200 rpms and at 70 mph, it is just cresting 1,600 rpms. Now, lets think about the horsepower and torque ratings of these two engines. Both are stock and in good working order and no modifications have been done.
130/240 is not a good horsepower/torque rating when compared to the 315/340 rating in the same format. Her Tahoe seems sluggish at times but has the option of dropping down a gear or two when needed. I doubt you will find what you are looking for by adding an overdrive trans to the M1009.
The M1009 should have a TH400 in it as supplied. If there is something different, tell us what is in it. Respectfully, Joseph.