Ive been playing for about 10 months now and Im trying to play hallowed be thy name by Maiden. At this point I dont intend to do the solo cause shred is beyond me at the moment, but the rest of the song is easily within my grasp.

The thing is that though I can play the riffs at the required speed or faster, during the pull-offs in some of the riffs, my thumb muscle really hurts, like it burns or something where my thumb meets my palm. I mostly played the acoustic until about a week ago and the pull offs on the acoustic never hurt, albeit they were never played this fast. What should I do? I think Im pressing down too hard for the pull offs (on the little jerk you need to do the pull off), but I dont know how to do the pull off without the jerk.
I think it's because your neck is actually a bit too thin for you, you don't have enough to grab a hold off, so to speak. To make it worse, I think you're actually cramping because you're putting way too much pressure on your thumb; pressure which really isn't needed.

Try this: play a few scales using only your finger pressure, so keep your thumb off the neck. This should tell you how little pressure you actually need, and will help you when you're using your thumb again. The goal is to use your thumb as a support, a bit of anchorage if you will, but to rely on your fingers for the pressure work.

Alternatively, it could very well be due to a bad guitar posture; are you standing, or sitting?
I was standing. I cant play too well sitting down. That way Im used to playing the acoustic and the electric's way too thin. My hands are big, but I dont know if they're too big for this neck though. If I wrap my hand around the neck my thumb can touch the middle knuckle of my fingers if thats any help. How do you know if your hands are too big?
Alright, well, if you're standing, it might be because you're guitar is slung too low? How low do you have it, like, under your waist, or more on your stomach?
Playing guitar is all about being comfortable, if you're have pains through your hands/wrists/elbow this is usually a very bad thing. The general rule: When in pain, stop. Find out what's causing the pain, then fix it, then return to playing.

Still, try using the technique I described earlier; this will help you release some pressure in your thumb/hand.

Also, hand size isn't really an 'issue', what I meant with the neck being too thin... well, it's hard to describe. It's quite common however that people who play like Ibanez Wizard necks and aren't used to them, cramp up completely. You mentioned your acoustic (which probably has a thicker neck), and that you don't feel the pain there, which led me to believe a thicker neck might actually be better for you.
But still, look at Hendrix, his hands were huge, and they hardly limited his playing.

Note, by neck thickness, I don't mean how wide the fretboard is, I mean the how far your thumb and the fretboard are apart, so to speak.

Oh. My thumb's about an inch away from the fretboard. I had the guitar on my stomach and my hand about chest high. And you're right, I was putting a bit too much pressure on my thumb, tried to ease it off and a lot of the discomfort is gone. Is there anything else that I could be doing wrong? Thank you so much!
It turns out I had my guitar slung too high. Lowered it a bit and its perfect. Doesnt hurt at all. Thank you once again.
Quote by hitman_47
It turns out I had my guitar slung too high. Lowered it a bit and its perfect. Doesnt hurt at all. Thank you once again.

Sure, no problem.

Remember though, always stop when in pain. If it hurts, you're doing it wrong, and it could grow into serious medical issues if you play through the pain.
If you feel any pain stop playing and rest, you shouldn't feel muscular pain or joint pain while playing. STart to play only when the pain has susided, you can do long term damage to tendons etc and end up with RSI or carpel tunnel.

You will notice however that the longer you play the more comfortable it will start to feel, until you can pick up your guitar and jam away for 4 hours without effort.