Squeak while accelerating.

Hi,

I have a 1994 Ford F-150, 185,000 miles, 5.0L V-8 engine, 4 wheel drive, automatic trans.

I have noticed an obnixiously annoying squeak that appears to come from the rear of the truck, but only when I accelerate. In attempts to solve where the squeak is coming from, I have replaced the rear brake drums and shoes and lubricated them. I have also noticed that I have a slight leak in the rear differential. I am wondering your opinion on this before I get my arms deep in grease taking the axle assembly apart to see if the problem is somewhere in there.

Could it be that I need to fix the differential or do you suspect the problem to be elsewhere?

Thanks.