I have a 2002 Ford Ranger 4 x 4 I replace the shocks has an alignment and new tires aluminum rims but I still get that shake at 65 to 70 mph goes away at about 74 mph really irritating

 

Is vibration is only felt in steering wheel or seat as well?

On an '02 you should have 1 piece rear drive shaft so no carrier bearing.

I assume you have tried coasting in Neutral at those speeds and also had the vibration so not related to engine or torque converter RPMs.

 

Ball joints?

 

I have the same issues, but I've done the wheel bearings and replaced the shocks , the ball joints were done , and didn't get an alignment yet..... the tires are bad, they need replacing, will do after the alignment... but I can't help feeling that its something else...... will let you know once its been aligned...

 

Vibration that exists at a certain mph and then goes away at a different speed is usually the result of a bad balancing on one or both wheels. Get a dynamic balance done ( The wheels are balanced on a machine that turns the wheel fast) and you should be O.K.