Volvo XC70 automatic gearbox problems

My XC70 has a problem with the auto gearbox. It is an intermitent fault that only occurs mainly when driving slowly..ie in town etc. It seems like the gear box is hesitating inbetween gear changes and when it does go into gear it jumps forward quite violently. A couple of months ago while tow my caravan in the lake district the rev counter went off the clock and I lost all drive. A fault showed up as "transmission service required". I managed to limp to the campsite we were booked onto (luckily only half a mile away) and unhitched the caravan. I started the car again to park it up and the fault had gone off the display albeit the engine management light was on. I decided to try the car along the A66 without the caravan attached and it drove perfectly, better than its ever done. Again, I decided to risk driving home on the monday and again the car was faultless. However, after a couple of weeks the "jumping" between gears started again and yesterday I was driving in a built up area and the previous fault occured again..the high rev's, the transmission service needed etc etc. Fearing the worst, I've tried to source another gearbox on the net and found one..at quite a high cost I might add..but the guy I spoke to said that it would be very benificial for me to take the car to a Volvo dealer first to put it on the diagnostic machine because these "earlier" XC70 gearboxes have a "known" software fault which causes the engine not to talk to the gearbox. Apparently this fault was rectified for the later boxes. Anyone got any info on this please. Thank you...John