If he is not lame, then he has been subjected to training techniques that have corrupted his stride. He probably knows how to do the super slow lope without four beating but that takes a lot of work on his part. Probably since you don't know him, and don't know how to "make" him do it, he's not giving you any correct gaits or proper transitions. Either that or he is getting arthritis or other age related issues where he can't physically perform that slowly anymore - you don't say how old he is.
If you want a pleasure horse, you may need the help of a trainer who can get him to pick up the gaits cleanly and stay in them for you. Right now you are just practicing very poor quality gaits with incorrect stride, rhythm and timing.
Personally, I don't like this type of training that emphasizes super slow gaits that are difficult and unnatural for the horse, but that's just a personal opinion about WP. What I would do with this horse is get him to move out with an emphasis on a true three beat canter, and find the speed where he can get a very consistent tempo without too much effort. Then if you wanted him to go slower from there, you could work toward it, but always having him move out again if he lost a true three beat gait.
The idea of him not being "forward moving" is mostly due to mental block from his past training rather than physical conformation. He has not been allowed or encouraged to move naturally, so is trying his best to do what the rider wants, even if it is very unnatural and uncoordinated.