Heat and age cause the O rings and other seals in the tranny to slowly get hard. They dont seal well and things begin to change. Your observation about the problem getting worse as the temps went down would support this idea. Even though you dont have a lot of miles on the car it is possible that the tranny needs to be overhauled. Fresh rubber pieces make a big difference in the shifting qualities of that tranny.

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I got too many cars!! Insurance eats me alive. Dave

78 Corvette Stingray - 3k
82 242 Turbo Volvo - Manual - 270k
86 300e 5 speed manual - 210k
87 420sel - 240k
89 560sl - 78k
91 420sel - 205k
91 560sel - 85k
94 GMC Suburban - 90k
97 Harley Davidson Heritage Softail - 25k
00 GMC Silverado 1 ton 30k