My 82 is making a loud noise. It starts right about 45 mph which is about where it goes into 3rd gear. If I let off the throttle or if I increase the throttle it goes away but when I try and run any steady speed above 45 it makes this loud noise. My truck is very loud to begin with (there are mufflers but they dont really do any muffling just there in case I get pulled over I can say I have mufflers) and I can hear this noise over the exhaust. Any idea what could be causing it.

Noises can be tough to diagnose. It could be from your engine, transmission, or your differential gears. Can you give a better explanation of what type of noise it sounds like.

Can you get the noise in both manual 3rd or 4th?

If push comes to shove, you might want to take the differential cover off and check for wear and looseness including the pinion shaft bearings.

hard to diagnose with out hearing. hard when you hear it. i've had a couple trucks with 2 piece driveshafts make noise at certain speeds when the steady bearing went

The best word to describe the noise would be howling. I cant get the truck to make the noise when parked to be able to figure out where it is coming from. I only have 3 gears. I think it is further forward than the rear differential. I could unlock the front hubs and leave it in two wheel and that would tell me if it was the front. I can check the steady bearing too and see if it has any play in it.