A couple of statements you made seem like cause for concern. You said you sprayed brake cleaner on the shoes, does this mean they had oil or grease on them and/or they are not new. If they had gear oil on them from a leaky rear seal no amount of brake cleaner is going to help as the oil will leach through and cause a problem like you described about the rear locking up. It's a lot of work to pull the rear drums on that truck so everything should be new or serviceable the first time.
Also, doesn't that truck have self adjusters?
Fred
