4 wheel drive
 

on a 88' xlt, do all4 tires spin while in 4WD ?

I don't believe a locker/posi is available for the front diff. but you can get them for the rear, check you diffs for t he code numbers and post them. I'm not into 4wd much so maybe some else can confirm this

There's a regular differential up front and maybe a limited slip rear differential in back, so you'll have a minimum of either 2 or 3 wheels driven, respectively.

L/S was optional for the front. Not many got it.

Really? The 1988 factory manual makes no mention of a front axle limited slip differential, either in the "identification codes" or in the "axles and driveshafts" section.