I have a 1997 Plymoth Grand Voager and if you put up both passenger and driver side windows at the same time the passenger side goes up really slow. If you put up just the passenger side window its slow in comparison to the driver side but not as slow as when putting up both windows. Could it be the motor or could it be getting less power for some reason and not making the motor work properly. How would I check to find the problem so I can fix it?

With any electrical problem, start by removing and fully charging, or replacing, the battery. Most auto parts stores will test and charge batteries for free.

If the problem persists, check the regulated battery voltage:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-10.html#post1973613

The test may indicate that the alternator is marginal.

The power window motors are probably getting the same battery voltage but one window motor is working harder than the other to do the same job.
Begin by inspecting the track the window runs in. Make certain the track is fulling into the channel and relatively clean.
With the window fully down, use a quality silicon lubricant spray with the straw attached and spray the lube directly into the window tracks, front and rear. Begin with the straw at the bottom and while spraying move upwards so the entire track get some lube. Work the window up and down a couple times to spread the lube around and compare the operations again. With any luck, you'll see major improvement.