Unsatisfactory grilling

I have used this grill twice since purchasing, both times completely unsatisfactory trying to grill steaks. I preheated over 10 minutes as directed, then added the steaks, once strip steaks about 3/4" thick and the second time delmonico's about 1" thick. Each time, it took at least 10 minutes per side to brown and in total at least 20 minutes to cook them medium rare. Some parts at the outside edges were even very rare at this point. This is totally unacceptable.

Please advise.