8.8 axle question

The rear axle in my 1994 f150 has a thicker casting at the top of the housing than any other 8.8 axle I have. Is this a provision for speed-o drive or what?
The truck came from the factory with a 5.8, automatic and off-road package. It has push button 4x4 and when in 4 wheel drive it acts like the rear axle locks. The way the inside tire starts skipping. Did they offer an option for a locking rear differential in 94?

Not that I am aware of. Convention limit slip. Ring gear speed sensor for antilock brakes likely.

I hope that is where the speed-o drives from as well. Cause I'm switching out the overdrive factory transmission for a full built C6. I want to keep the factory gauges working.

Last I remember the speedo was driven from the rear end. Check the trans tailshaft. Should be a plug stuck in there. Mine was a 94 ex cab with 5.0 and full Cali package...