Not sure if the Isuzu's are the same but looks more like 2.00:1 for reverse.

A locker of some sort will help in both directions. If you are revvin gup to 2000 rpm, it sounds more like a traction issue than a tranny issue.

Gear Ratios:
2.40:1 1st gear
1.479:1 2nd gear
1.00:1 3rd gear
0.723:1 4th gear
2.00:1 reverse

Optional Gear Ratios:
2.86:1 1st gear
1.62:1 2nd gear
1.00:1 3rd gear
0.723:1 4th gear
2.00:1 reverse