Yep, it looks like you're definitely on the right track now. Your groupings are pretty much typical of what you can expect. As you indicated you won't win any 500 yd competitions with a Trapper but it sure is a heck of a fun gun. You can still experiment around to find the right load that is in tune with your barrel.
I'm glad you posted this because I forgot to tell you the results of my experiment. I loaded some light loads (6.0 Bullseye, 250 RNFP) and shot them at 30 yds. out of my 94 with a 20" bbl (same 1:38 twist as the trapper). Each hole was a nice ellipse of about .45 X .55. The bullets were obvious wobbling. So this settles it for good - no wimpy loads allowed. An interesting phenomenon was that the majority of the ellipses were all aligned in the same direction, approx. NW to SE on the target. I guess this means they at least wobbled uniformly.