1988 Dodge Van Passenger door

Since you have the panel off, run a pair of wires from a battery directly to the motor. If it runs at normal speed, you'll know the motor and tracks are fine. If it's still slow, spray silicone spray lube in the rubber window channels. That's an easy way to overcome gummed up sticky channels.

Common places to look are BOTH window switches and the wiring between the door hinges. Check operation from the passenger's switch and from the driver's switch. If the window works normally from one switch, either switch could have burned contacts. Assuming the driver's window works ok, you know the 12 volt feed wire and ground wire are ok. There's a different 12 volt feed wire in the right door, but the ground still goes through one of two wires between the door hinges, over to the driver's switch, through one of two pairs of contacts, through that ground wire. A single frayed wire between the hinges will make the window run slow in one direction from the passenger's switch, but both directions from the driver's switch.

When diagnosing an electrical problem with windows, it's important to understand that both switches are involved. When both switches are at rest, you can use an ohm meter to measure resistance from any motor wire, (unplugged for accuracy), to ground. They all should read very low, (ideally 0 ohms). There is one problem with this test. All it takes to get a good reading is one remaining strand of a severely frayed wire, but that one strand won't be able to handle the current needed for the motor to run at normal speed.

When either switch is pressed, first one of the grounded contacts breaks open, then the terminal touches the 12 volt contact. The current returning from the passenger side motor goes through the at-rest contact, through both sets of door hinges, through one at-rest contact in the driver's switch, then to ground through the ground wire in the driver's door harness. Those "at-rest" contacts could be burned or pitted. That's why either switch or wires between either door hinges could be the problem.

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