engine 500sl 92 help!!!

my 500sl engine shuts off some times after a 100 miles or so of hiway driving. and looses power also, after it sits will crank fine, when stone cold,and run ok maybe a lil miss, Do u think the egnition coils are going out all else has been replaced much, when u stand on the gas little response. nothing kicks in. has a tune up and new wires already, im discuted !! help, the coils are 110 each i see, can it be they get warm and spark breaks down ?? help help !! also is there a limit to how fast the command mod will let the go ? i was told by a mech. it has . is he jerkin me on that stuff?