Sounds like your 2 spd is not working and are staying in low, or that thing has some serious off road gears.

can also look into a axililary trans,
spicer made 3 auxiliary transmissions for chevys according to the info packet for my 69
7231-a 3 speed .74
6041 4 speed .86
7041 4 speed .83

Enjoy life, it's the longest thing you will ever do