Get a new headcleaning tape is my first thought. They're good for about 25 passes and then that's it. Also, what did the Hi-8 footage look like? Was it clean or did it have noise?

Try this. After you've cleaned the heads, fast wind the tape you want to play all the way through and then rewind it. The freezes are dropouts due to data errors. DO NOT play the tapes until you've cleaned the heads. You run a very real risk of damaging them. Also, how many times have you reused these tapes? It could be that one of your tapes is shedding and seriously clogging the heads.

Finally... it's an issue in the DV world, not sure if it applies to Hi-8 or not but you generally do not want to switch brands of tapes. Some brands use a different lubricant type (dry vs. 'wet', it's not really wet it has to do with the manufacturing process) and switching between them causes the tape transport to gum up and the heads to get dirty very quickly.