Originally Posted by HappyTrails
He was asking about 5.38 gears and the pinion, not D44 vs D30.
The only difference between a D30 and D44 is the differential housing size, no strength differences. So, my point is valid by speaking of 5.38's in a D44.
Well, the OP has a D30JK and he was only asking about how feasible/reliable it was to use 5.38's in a D30JK. Talking about D44's in this case just muddies up the water IMHO.
Again, to the OP, the fact is the pinion gets so small on a D30JK (that's what I have) even with 4.88's that I'd personally be very hesitant to go any lower (unless she's a pavement princess...). Not a hard-and-fast rule: opinions and results will vary widely with experience and use, however.
Not to dismiss HappyTrails - upgrading to a D44 front, however, would be a better option if 5.38's was the preferred gear range.
ALSO, as I said before, if the OP is going 5.38's - I can imagine that the DESIRED tire size is also going to be HUGE - which presents many other problems other than just small pinion size (especially on a stock Dana D30JK). IMHO, 35's are the max size for a D30JK that can be run *reliably* - and that is with sleeves and gussets whopped in. If you want bigger meats, then (IMHO) you'll need a bigger axle. Again, opinions and results vary widely with experience and intended use.