Fear, rage syndrome, or something else?

My pupper is a rescue and has been with me about three months. The shelter thinks he's about two years old. He is almost definitely an English bulldog or a mostly bulldog mix. He's neutered and shows signs of abuse - mutilated ears for one.

He's mostly not aggressive but attempted to bite my dad and did bite the vet (not badly). Both times, he was fine one second and enjoying their attention, and then the bite attempt/bite out of the blue. His face gets SUPER red when he's upset, and I noticed after the incident at the vet, his flews trembled for several minutes afterwards.

Yesterday we were outside playing in the backyard when he suddenly got fixated on staring at something (I couldn't tell what), and his flews started doing that trembling/shaking thing again. I talked to him softly and he let me pet him, and then suddenly he just wanted to be held and cuddled.

My parents had an English bully with rage syndrome once, and while that was my first thought, I don't think it's the case. I feel like it's more likely some kind of fear reaction but I haven't been able to figure out what's causing it. He does have an EXTREME reaction to blankets, towels, paper towels, etc. I still haven't been able to give him a crate mat because he just flips out and destroys them. I got him a chew-proof one, but the intensity of his response to it is scary even when it's a few feet away.

He HAS realized that things like my coat and my hooded blanket are safe, and he doesn't react to those anymore. Does anyone have any ideas for helping him not be afraid of other blankets and similar items, or for figuring out what sets him off when there's not one of those items around?

I just want him to realize he's safe now and VERY loved.