Also, make sure Cower is off. I haven't played my Hunter for a few months but there was a bug where Cower kept reactivating even if you turned it off. With Growl on and Cower off pet aggro is usually quite good and you shouldn't be losing aggro to a healer on normal mobs.

If your pet is trying to tank multiple mobs, be careful to get pet aggro on all mobs before you heal. Thunderstomp is great for this but if you don't have that talent then you need to manually switch targets to get some aggro on each mob you are are tanking.