Here's how it goes - he see another dog and barks - sometimes playfully, sometimes not so much and sometimes he growls along with it all and pulls, but after he watches the other dog for a few seconds, he starts whining and tail wagging and doing his play bark, but occasionally still growls a bit? Once he gets up close to another dog, he starts sniffing, and jumps back...like he's scared. He was raised with another female pit that he gets along with very well, his previous owners took him to a dog park once with no problems, and while I've had him, he's met a cocker spaniel (who TOLD him! he was scared tail between his legs hiding behind me till he got enough courage to sniff it's butt and got snapped at), a lhasa apso and a boxer, all of whom he initially growled at and them jumped back and acted unsure about once he got close. There was also a guy who let his dogs approach us on a walk one day - a golden, a lab, and some kind of mix - 2 of which growled a bit, but just sniffed him while Reno froze. He also met some little black fuzzy thing that ran out of some guy's house, and Reno just sniffed him, and froze up again.
SO....what can I do? How can I socialize him?

Any suggestions? How bad does this sound to you guys? I've had a dog previously who was neurotic and scared to go around other dogs, so I'm used to avoiding animals on walks and so on, but when you have a pit growling at a passing person with a dog, it's a bad representative of the breed and us personally as his owners.