Tom
Hello & Welcome to the Forum!
That GP-20 is a nice locomotive.
There are a few of us here on the forum that are multi-scaler's who play with Large Scale as well as the smaller scales. 

There are R/C control systems available that you can plug the receiver in between your power supply and track available & have a hand carried transmitter for control.
G Scale Graphics
http://www.gscalegraphics.net/store/p54/10_amp_Trackside_R%2FC_%28Transmitter_%26_Receiver%29.html

AristoCraft/Crest offered their Basic Train Engineer (stop/go, speed/forward/reverse) before they went out of business. They can be found fairly inexpensively at the online auction sites.

There are R/C type control systems that the receiver is installed in your locomotive, using batteries to supply power to the locomotive.
Radio Control Systems
http://www.rcs-rc.com/
Airwire
http://www.cvpusa.com/
Crest Electronics.
http://www.crest-electronics.net/

R/C & battery means never having to clean track again.
Track power means never having a dead train because you forgot to charge the batteries.

The referenced systems are some of what's available in C.C. that I am familiar with.
Me, I'm a track power/analog guy, but I do have a Basic TE & 18V battery that I use in my B-mann 45 tonner for pushing my snow plow.

Happy Rails!
       &
Merry Christmas!

Dave