Update - it's all fixed. Didn't have to buy another motor.
In case anyone is wondering, I had to ask Lippert and got confirmation that the Venture motor and gearbox is a drop-in replacement for the Toula on my chassis. Don't buy direct from Lippert as their price is $500+. Instead see previous posts for links to retail websites for the same unit for about $250.
I ended up cleaning the commutator with a fiberglass "pen" (small brush) and electronics cleaner. Here's me just getting started on it:
Polished everything up nice and sprayed out the gunk. There was certainly some gunk in there. Reinstalled and the slide moves as quick as the others now - thanks everyone for the tips!
I also fabbed up something quick for manually running the slide if it ever happens. I just got some square tubing (3/4" I think) from Lowe's and cut a notch into it to work with the manual slide rod. This fits nicely into a 7/8" socket and with an extension I'm good to go with using a drill instead of hand power.
I plan to update this by getting a friend to weld a 3/4" bolt on the end somehow so I can just use the 3/4" socket drill adapter I use for extending/retracting the manual stabilizers. Hopefully I never have to use it ...