I'm wondering if it isn't due to whatever Accushift shifters you're using. When I originally got my CrissCross, the 7-speed Accushift setup there (flat bars, shifter pods) drove me nuts. It absolutely would not hit the middle cog. Shift from 3rd to 4th (on click) and it'd go to 5th. Then you'd have to do a second click to properly line everything up, on to 6th and 7th normally. Go back up the cluster, and once again it'd jump you from 5th to 3rd, then do another click to take up the cable and line up everything properly. Shifting to 2nd and 1st went normally. On the rare occasion you'd get it to land on the 4th cog, it'd jump off within a couple hundred meters.

I finally got disgusted and replaced the whole setup with Alivio/STX indexed, and haven't looked back.

When I got the GT Tachyon on the road, it didn't have a rear derailleur to go with the 7-speed Command shifters. So, I held my breath and pulled the SunTour out of the parts bin and hook it up. That combination worked perfectly, is still working perfectly now, and I don't look forward to any problems in the future. Go figure.