Cartridge Tacking Problems - Help please

I have major tonearm/cartridge tracking problems that seems to have gotten worse, leading me to believe there's a problem with the arm. Can anyone suggest what I can/should try to further diagnose the problem?

Here's what it's doing:
On some (becoming many) discs, the cartridge will just skip out of the track, as though there's a scratch, or someone bumped the stand. Changing the anti-skate setting (ie over driving the anti-skate to 2.5) helps a little, but doesn't cure it.

Here's the set-up:
Pink Triangle original table
Audioquest PT6 arm
Signet TK7SU cartridge with new stylus
(the the problem exists also with the old one)
I have no damping fluid in the trough at present

Here's what I've done:
Table is leveled and set up properly
Arm/Cartridge is set up and aligned (and quadruple-checked)
Tracking force is set at 1.75 g, which is the max recommended by Signet. I've always tracked this cartridge at 1.25 g on my old table and it worked beautifully.

thanks in advance!