I have a '03 base model ranger 2.3 5speed. A week or so ago it started this vibration in 4th & 5th gear it starts at 45 mph and continues. It sounds as if I need to shift gears. The vibration is getting worse. The truck has 148,000 miles. I just bought it a few months ago so I have no idea when anything was changed.

 

Bad Drive shaft causes vibration. But not sure what you mean by feels like you have to shift.

 

Is it a rolling vibration or engine vibration?

While above 45mph if you push in the clutch and let engine RPMs go down does the vibration go away?
If not then it is a rolling vibration.

Could just be one of the wheels has lost a balancing weight, check each wheel inside and out for a "clean" spot where a weight may have been.

Block the wheels and put transmission in neutral, get under truck and try to move drive line manually if you feel it move try to locate a bad u-joint, it is usually fairly obvious, there is some play in the differential, that is normal.

 

Yeah, what RonD said. If you have one, check the carrier bearing as well.

 

I changed the u-joints yesterday and the rear one was very bad it seems to have fixed the problem. Now its on to the next one. When I hit the brakes the whole truck shakes and makes it hard to control. I am in process of getting brakes changed all the way around to see if this solves this problem.

 

You have a warped rotor on one of the front wheels.
It is often best to replace both.
You could have lower ball joint or tie rod end issues but warped rotor is more common.
If you remove the wheels and calipers then turn the rotor you will see it move in and out, so warped.

Rotors are what the disc brake pads push against to slow you down.
If they get too hot the metal in the rotor warps.
They can get too hot if a caliper is sticking, i.e. not releasing all the pressure when you take your foot off the brake
This rubbing heats up the rotor while driving and when you do use the brakes that extra heat causes the warping.

So good idea to replace calipers if you have a warped rotor.