'07 xterra had low to no power when accelerating from 40-60 mph

scan it , it will tell you why.
if TBW fails throttle by wire fails speed is like 20mph max or less. on purpose., so scan it.
also if RPM is low foot ******* the throttle.?
then engine power lacks, scan it.
if RPM goes way high but MPH not same increase,the transmission is dead or slipping.

Club Xterra is very helpful:
Whine on acceleration Nissan Xterra Forum

There are some youtube vids as well:

Bad idler sensor possibly or abs sensor

possibly the crank shaft sensor. i had to help a family member with a change on a xterra with same issues and it fixed problem. but a mechanic will be the best one to ask

problem is electronic but exactly what i have no idea without my head under the bonnet ,try the dealer as it may be cheaper in the long run

check the u joints in the front drive shaft

low speed shakes indicates a wheel alignment problem
have the suspension and wheel bearings checked out by an accredited suspension shop
under acceleration it could be engine mounts cracked in the rubber being actuated by misfiring form a cylinder
run the fault codes as well

Well if you would elaborate some more on what kind of car you have,...that would be helpful as my ESP is very low today....

have you tried having your fuel injectors cleaned on it. the engine might not be getting enough gas at take off. it might also be that your gas tank fuel pump or the other fuel pump going bad

had the same problem it was the u joints....if you get a vibration at higher speeds that will also be an indicater...on the 2005 exterras you have to replace the whole drive cshaft fortunatly min was under drive train warranty.