I agree with Jed M that this sounds a bit strange. Certainly, DTS soundtracks are always about 4dB "hotter" than Dolby Digital (that's one reason that is often sited for the perceived benefits of DTS), but they shouldn't be 13+dB louder. I tried Gladiator briefly this morning. I couldn't crank it up real high since the wife and daughter were still sleeping, but I estimated that I needed to drop the volume probably around 6dB or so when using the DTS track. I used an SPL meter to try to get the two soundtracks adjusted comparably because of the need to keep it turned down a bit and because the way that disc is mastered makes it difficult to flip back and forth quickly - the "audio" button on my DVD player's remote was disabled, and I had to go into the disc menu to switch between tracks (making it very difficult to rely on my ear alone to match the two tracks up). What I was seeing was fairly typical for a DTS track (possibly even a little moreso, which might suggest that the Gladiator DTS track is a bit hotter than usual) - and that does not match your experience at all.

I'd suggest taking a stab at calibrating with an SPL meter. If you are still having trouble getting the expected output, give Outlaw a call and see if they can help you find anything that might be messing with you.