Truck shakes at 60 to 70 mph

Whenever I drive up hill or at an incline driving 30 mph or faster my truck will have an inconsistent slight shutter or vibration that I feel in the seat and floor( when driveing on highway doesnt happen at all or very rarely). There isn't really anything else that will trigger it like specific rpm or specific gear(im sure it could be the lower gears if it is transmission). Ive changed the driveshaft u joints, serviced transfer case (it was slightly dirty and no metal fragments), checked the diff fluid( no metal fragments and fluid looks good). Looking for any information on what it could be or where I can find a repair/maintenance guild for my vehicle? Any help would be appreciated

So when I’m around 70 I can fill a small vibration but when I left off the gas it just echoes and vibrates but it does this anytime I let off the gas and start to just let the truck start slowing down.

Makes a noise almost like when you’re on the highway, and getting out to the side. It has those things that wake you up if you falling sleep, and vibrates. Just like if you run over those rumble strips, but it feels like it’s coming from my rear tires.

Shakes and won't start ive change some of my fuses and now it shakes