Is my horse lame or just stiff?

I have two horses, and one horse I ride almost everyday, but the other horse was just to much for me to handle so I put him away for a while. After 2 years of being in the pasture I finally got him out again for a ride. He seems fine except the fact that he's so "stiff" that riding him feels like you're on a roller coaster! He seems very stiff and his gait is horribly choppy and it's a very bumpy ride. I'm just wondering, because I'm not quite sure if it's just from not being ridden for so long, and if he actually is just stiff, or if he is lame. He doesn't refuse the saddle, and he hasn't tried to throw me off, buck, or rear. He isn't foundering, and i can't really tell if he is favoring a foot or leg. So just give me some advice please, do you think he might be lame?