Well Dude,
Either your healers are inadequate, you are inadequate, or both. I have been almost 100% healing spec. I have a tanking set that is uncrushable, but doesn't have as nearly the same stamina. But my experience healing hopefully will give you a few pointers.
1) Any healer who thinks they can HOT you, or chain cast fast heals in heroics on you, and get the party completely through the instance is wrong. I can chain cast FoL in heroics ONLY when a guild tank (or one I trust) from SSC and TK comes along. I remember my first heroic instance healing, it was a pug, and it was 3 MS snot-nose warriors from an uber guild, and a mage. And it was the fastest instance I have ever completed. I was COMPLETELY on my "A Game" for one, and two, I couldn't stop to breathe between chain casting Holy Light.
Ditch the douche-bag healers.
2) As a healer, I have found that I can participate (with my current gear) at levels that are above my gear. I wouldn't directly say it's my lewt skills, but I won't be burning my DKP until the rest of the guild gets a little more geared. That said, a healer that is healing you, and has good skills, should inherently have an easier time, because healers (out of the possible roles of Tank, DPS, CC, and Healing) can lean against their skills to offset some of the deficiencies of being undergeared.
Ditch the poorly skilled, douche-bag healers.
3) You also have to understand the common PUG mentality since they eased the rep requirements to do heroics. There are MANY more poorly geared people pugging. That said, poorly geared paladin tanks have the same stigma as used-car salespeople. It's so terribly difficult to get enough stamina while not sacraficing mitigation, that you can't evenly and consistently progress. This is the proving grounds of future paladin tanks. You will be (and feel) UNDERGEARED, then miraculously after 1 or 2 pieces of badge gear (and subconsciously improving your skills), you will break into the "doable" zone. I've done it, and I've seen it.
My recommendation to you, good sir, is to:
- Keep clearing Karazhan on the weekends. 22 badges a clear!
- When pugging heroics, clearly state to the healer in a tell (nicely and before starting) that you as a reasonably geared paladin tank require large heals almost exclusively. If you get a "duh" response or something more positive, then ride the karma. If you get a stuck up response (especially with someone of equal or lesser gear value), politely bow out and say it's better for the party if you bow out, and thank them very much.
- Try and arrange heroics ahead of time with guildies. They will help you get through this awkward pubertic paladin phase.
- Farm with mining and pay for the better gear. Yeah, it really sucks when you buy all new gems and enchants, but this is an advantage you can get spending your own time, not the time and patience of PUGs.
- If all else fails, entertain the idea that tanking with a paladin may not be your calling. Paladin tanking is very difficult. You need to juggle every option you can, from your Avenging Wrath, to periodic mid battle Avenging Shield tosses, to timing your Holy Shield down to the 10th of a second (sometimes) to always having consecrate down in all ideal manners. Even if you can get all that down, making sure your talents match your play style, and your play style matches those you group with are equally important. I know well geared tanks (18k hp buffed, uncrushable, 350 +spell damage, +5% hit rating) that can't seem to rope their brain around USING EVERYTHING THEY HAVE. It's not their fault, either it's a lack of practice, or it's a mental thing, either way, sometimes you just can't get it all together.
Final thought: It sounds like you can make up some of these problems with some better skills. I'm not ragging on you, but paladin tanks are born with lewt aggro. You gotta use everything, brotha man, EVERYTHING!