why does my truck starts shaking when i’m going 55 to 60 mph in the high way?
You may simply need to have the tires balanced.
Or, you may have worn front-end components on this mystery-vintage Xterra.
Or, you might need new tires if they have “slipped a belt”. However, the probability of all 4 having a slipped belt is unlikely.
You can really help yourself to get a better response if you will tell us:
How many miles do you have on these particular tires?
Are the rims OEM, or after-market rims, and have you ever hit a curb?
The mechanic has looked at it and said you need new rims and tires. I assume you have some bent rims?
I have no cause to disagree with the mechanic from this distance. Bent rims and tire with abnormal wear can easily cause your symptoms. I’d want a good look-see underneath the vehicle too, to look for a possible cause of the abmormal tire wear.
Get another opinion. Do you drive off road? Have you hit some big potholes or curbs? Bent rims are usually pretty obviously damaged by hitting something. Certainly a bent rim will cause a shake, but it isn’t likely that all 4 rims are bad.
Old tires can have the tread and tire belts separating, this will cause a shake. Out of round or out of balance tire(s) can cause a shake.
When the shake comes from a front wheel you’ll generally feel it in your hands coming via the steering wheel. A shake from a rear wheel you’ll often feel more in the seat of your pants coming throught the seat cushion. All it takes is one tire and/or wheel to be out of whack to cause a shake.
A steering system in poor shape, worn suspension parts, out of alignment are also things that can cause a shake even with OK tires and wheels.