Powerglides have around a 1.76/1.82:1 first gear, and a 1:1 second gear, no OD, and no low 1st gear. Also, they are really only strong if you have a race built one that replaces every single part in the thing with an aftermarket piece, inluding the case, which can cost upwards of 6 - 7K for a bulletproof one. Great for drag racing, but probably not the best for your truck.
I think if you put a billet input shaft, along with the billet intermediate shaft, and billet forward hub in your truck, it would be plenty strong. Those pieces will probably cost you around $700 or so. It might be cool to put a transbrake in it too! I put one in the 4L80E in my car and I love it, awesome launches at the drag strip, but doing so made me think how fun it would be to have one in my truck for the sand races.
This guy specializes in 4L80Es...
http://www.jakesperformance.com/4L80E.html
I bet a stage 3 would solve your problems. If you call him and tell him whats happening and how you use the truck I bet he could make a reliable 4L80E for you.
A lenco would be awesome too! But big $$$. Also, you may be treading new ground putting a transfer case behind one. Combine a lenco with a triple stick doubler case though and you could get the prize for the most shifter sticks in your truck.