Unfortunately I can not help to much on soloing Sulf and Gole as I havn't had the 2T5 to try those myself.
Sulf:
I assume running out of 60yd range to try bandage on Sulf doesn't work?
Gole:
Could you try timing a couple of distracting shots from long range to keep him running long enough for the debuff to fade?
(Same thing as we do on Kurinnaxx)
Ragnaros:
I keep pet on passive/stay right under Rags and direct him to attack myself so that he will not try save me from sons and get onto their agro list.
When it comes time for the spawns I let a few spawn, then just as the first nearly melee's me I cast deterrence wait until thats about to drop then I FD.
The reason for that is that they only seem to despawn if they agro'd onto you which takes them a few seconds for them all to do.
Depending on your positioning some of them will not agro even using Deterrence. (I stood
here infront of that rock)
If you are lucky these ones will stay put the entire fight, if not they might agro randomly later, especially if your pet does a stupid move and gets close to them somehow.