Dodge: Riding with brakes, pep boys, brake job

Question
I have a 1988 Dodge Ram 50 2.6 Liter manual transmission truck. Recently, I've been having problems. Sometimes when I drive the truck, the trucks acts as if the brakes are on. I normally can press the brake pedal nearly to the floor, but now the pedal will hardly move at all. When I take the truck out of gear that truck immediately slows does as if the brakes were on. Also, when I am in a high gear, I can sometimes feel the  truck pulsating as if the brakes were scrubbing against the wheel at one point. These problems are not present all the time though. On occasion, the truck drives like I think it should. The Pep Boys mechanics say my rear differential seal has a leak, but I am not sure if this is the cause of my problems. Any guidance is appreciated.

Answer
If you know someone at a garage that you can trust not to rip you off,take it to them and explain it to them.A differential seal will not cause this problem unless the fluid has leaked out,it would normally start a whining noise.Sounds to me like you have a brake sticking somewhere.It probably just needs a brake job.