i'm ambush/backstab shadowstep build on my rogue and i'm thinking about going mutilate build.....

Typically a good rogue can get me down to about 50% health before their stunlock breaks- this used to be a lot worse before I had 400 resil. Then, it's my turn. They're usually down by 25% to 50% their health in my first hit. Then come the stuns. Ret paladins have very little that requires any significant cast time, so interrupt isn't a big issue. The longest thing I'll typically try and get off in a fight is the 1/2 sec hammer of wrath. If I need to get off a heal to live, my first try is to repentance you, so you're stunned until you take damage, fire off a heal, then hit you with another burst before it ends. If you trinket out, and I have no other choice, I'll bubble and just finish you off- but I rarely have to use bubble in a rogue fight. Also, if I start at full mana, I never run out during anything as short as a rogue fight- it takes a good long battle with a high-resil healer to pull that off. Then I'm forced to switch to rank 1 seal of command, and use blessing of wisdom to avoid really running out. It hurts my dps, but not nearly as bad as having no mana.

On the other hand, I can't think of a ret paladin that's beat me in recent memory. I've coached quite a few, and they all seem to have silly talent builds and poor gear. It wouldn't surprise me at all if you beat pretty much every ret paladin you fight.