I pull a 2200 pound Boston Whaler rig all over New England (mountains and shore)with my 855 Turbo - with no bother. Don't forget the trailer: tires, bearings, lights and spare tire with jack and lug wrench that fits trailer. The car will do well with Mobil 1 anyway, and even better with the trailer load. I don't use synthetic transmission fluid, change about 4 quarts of it every other oil change so it is always fresh. However, I will probably go to synthetic this summer - can't do anything but help. I don't think the '95 or '98 owners manuals had any recommendation about transmission fluid changing, but our new '07 recommends transmission fluid changes every 50k or so if you tow a trailer, and also use of synthetic engine oil with trailer. On the road, keep the transmission from shifting frequently by holding it in third whenever useful. Heat is the big problem for the transmission, and it is reduced by fewer shifts and lower gears. The extra gas is not significant in the big picture.
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Mike Sullivan '07 XC70, '95 855T (100k), '95 855 NA (148k). Past Volvo's: '85 744 (256k), '86 245 (165k), '86 245 (195k), '88 745 (208k), '91 745 (196k), '93 965 (147k) , '98 V70XC (98k).