It's not the calipers. Everyone knows the design flaw on the rear calipers. For those who don't know the e-brake has a pivoting mechanism which has a rubber seal. The design flaw is on the rubber seal. These corrode over time and leave the bearings inside to rust. The result are e-brake's that won't release along with the parking brake lever. If your seals have not yet corroded than there is a chance to remedy the situation. Apply some water proof grease around the seal periodically to prevent rust and spray some WD-40 on there for good measure. This is a temporary solution but if you do it frequently enough and use your parking brake often (to execise the pivot) it should last you a while. Mine has not stuck for the last six months and I am able to park on a 40 degree incline (my driveway). One more thing also if your parking brake won't hold the weight of your car on an incline, there is a tensioner beneath the center console. The opening is to the left of your parking brake lever. Just pop it open and you should see it. Tighten it and you should be good.
Now that takes care of the caliper thing so what about this annoying deceleration. Sensor calibration problem or is the dreaded tranny? Like I said before mine is still strong and smooth. It just seems to drop a gear around 40 to 60 mph. The car will glide if you let off the gas at around 80 mph. I know the car drops a gear because I payed attention to the tach and I see it jump a few hundred RPM's to get back on the right gear when I step on the gas again. I've recently had my transmission flushed and all the oil replaced - no help. Somebody tell me it's not the tranny.
By the way if your an MX6 ATX owner try not to be scared of the horror stories Probe owners have about their ATX's (no disrespect to the Probes). I've been to probetalk a few times and I've read the frequent stories about Probe ATX's dying pre 80k mileage. These stories are nowhere to be found from MX6 ATX owners. In fact I've heard stories of post 120k ATX still going strong. Our cars may share many key components but from general observation, I think that it's safe to say the MX6 ATX fortunately does not share the probe ATX horror stories in particular. I've read many stories on guys who lose driveability on all gears (R, D, 2 , & 1!!!) before 100K That's insane... and also never usually told by a reasonable maintainer/driver of an MX6, especilly not at the mileages that they occur on in Probe's.
Well I've got to get back to some paperwork. Also try not to play with the HOLD button. Doing so will probably quicken the life of your tranny. The tranny is not meant to be switched gears on an instant at high speeds. The manual actually suggests flooring it (verbatim: "depress the pedal fully", if I recall correctly and the ATX will drop from 4th to 3rd gear to provide passing power.