Transponder check

I just took my Pegasus in to have the Trig T21 checked. The glider is relatively new to me and this is the first time I've personally taken it for the test. My former partner took it to the same shop two years ago and it passed and without comment from the tester, as far as I know. The guy doing the testing said that the power output was low - getting 35 watts while the glider was in the cradle, 65 watts at some point after we backed it off and some other, higher, reading a bit later after jockeying the test antenna around a bit. I don't know what that figure was. The antenna in the glider is a flat type that is mounted on the belly under the seat pan. The connection looked good but he cleaned it anyway. Its to the right of center line and the testing was done from the left, if that matters. He tried using his own antenna and didn't see any improvement. He did a fair amount of button pushing equipment moving and finally said, "I got it to pass but in the off season send it out to get checked." He also mentioned that the frequencies were a bit off.

I got the impression that he wasn't that familiar with the Trig unit or gliders. So, what kind output should I be seeing 4' from the glider? What could be causing the low output? The battery was almost, if not completely, fully charged. Why would the frequencies drift?