I'm hearing a very loud whining noise that starts when I hit about 45mph but as the truck gets hot the noise starts at a lower mph. At first I thought it was the tires as I am not used to the larger ones but the tires are not getting hot and look fine. Any suggestions?

Sounds like it might be a transmission mount or engine mount faulty

Possible bearing in one of the drive pulleys. I have changed numerous alternators for this noise. Take the belt off and start the car. If the noise goes away you know it will be pulley related and not transmission related. If noise goes away, spin all pulleys by hand to determine the defective/noisy one

Start at the turbo and check for loose or blown air lines . Check the intercooler for cracks. The turbo whine is normal but you would not be hearing it as the turbo is controlled to vary the amount of boost needed for the throttle setting. If you have to use starting fluid to start a diesel then it is time to consider a re-ring and bearings for the engine.

Head Gasket & or Damaged & Blocked Exhaust
Converter

Can't you mechanic diagnose & tell you all that?

one of the cabin seals has come lose or part of the plastic under the windscreen has a gap, can happen with plastic. just need to reseal the gap or refit it and seal at the same time. its body panel sealer can get it in a tube for a sealer gun or you can get the brush on type from most car part stores.

Theres many holes on the fire wall for the wires to come through from the engine to behind the dashboard, one could be missing the rubber around it or one could be missing, also you may likely have a leak on your windshield, you can get some black silicone and patch it with it, same for the dashboard.

could be a wheel bearing jack the side with the noise & spin the wheel

take it back to the garage that done the job and complain and make them sort it out for free ,its their boo bo as it should have been test driven and sorted before it was given back to you..if they refuse to do then be nice and leave ,then pay some heavies to go back again with you and ask again nicely and if they tell you to leave then bring your friends in with some tools in their hands

Find a quiet empty stretch of road. Go 50 mph, put the trans in NEUTRAL and shut the engine. If noise is still there, swing car left and right to detect noise differences. Could be hub or axle bearings. Not engine or trans if noise is still there. Hope this helps

lift the car up and check the wheel bearings by turning the wheels manually. Listen for any clicking noises. Move the wheel back and forth pulling it toward you. There is not supposed to be any movement or noise on the wheel if the bearings are good. if you do see any movement or hear any noises , replace the wheel bearings