His home run rate fell in 2004 when he claims he stopped using steroids (his first season with the Yankees). However, his power peaked again in 2005, and reached a career-high in 2007 when 11.4% of the balls he hit in play went over the fence.
In all, A-Rod has nine seasons in his career in which at least 8.5% of the balls he hit in play were home runs. And only three of those came during the years in which he admitted to using steroids.
We will probably never know the true extent of Alex Rodriguez's use of performance-enhancing drugs. But this chart does show that he had a number of seasons, both before and after, in which he showed a similar ability to hit home runs as when he admits to using steroids...
Data via Baseball-Reference.com