Does any one else with a 4Matic have problems with it being slow to back up in reverse? Mine takes a while for reverse to engage but when it does it feels real strong -- not like its slipping. Especially if I running about 1500-2000 rpm or so it will squeal the tires when it kicks in. I'm suspicious of the 4matic or its probably the transmission. Just turned over 151,000 miles on it.