Tracking force on Audio Technica 120Eb

First of all, your arm is medium mass which benefits more from cartriges with heavier tracking force than 1.4g. This can be compensated if the cartridge tracking force even slightly more increased from recommended settings. Try to increase to let's say 1.9 or 2g and see if there's difference.
I had similar deck set up with ADC type III cartridge that has 1.0...1.5g tracking weight that I had to set up to at least 1.8g to properly track record.
Tonearm is always part of equation.

I picked up a Sure tracking force gauge.  Can you recommend a strategy for choosing an optimal tracking force?  Lets say I try your suggested range of 1.8, 1.9 and 2.0.  What should I be listening for?  

Not only listening but also looking the way the cartridge tracks. You need to get that "button" where the traction isn't in exchange of sound.
I often may play warped record and see how stable it performs. Solo piano usually helps to hear various imperfections of playback. I test with inexpensive classical Denon series of recordings. I also use Super Analogue japanese pressings with piano music played by Ashkenazy, Cliburn... 

Just finished setting up Pioneer 117 similar to yours with AT120eb same cartridge. Found it tracks best at 1.75g.