Tom- check the portion of the slide tray where the actuator mechanism connects to the tray. On some units the tray cross piece flexed quite a bit, so a fix was devised to take two pieces of 3/8" allthread & connect that cross piece w/the next cross piece behind it, w/a nut on either side. Takes two allthreads of appropriate length, & 8 nuts, one on each side of each end of allthread; one allthread running fore-aft about 2" each side of the actuator rod.
To see this in action, you have to be under the coach watching for the 1st coupla inches of extend or last coupla inches of close. If yours has this affliction you will see the flex on the front cross member just fine. If no flex, then its something else, perhaps as described above.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project