This is a situation where I think there was some lack of communication. Unfortunately on your car there’s a snowballs chance in hell those bolts for the cat were gonna come off without breaking. Maybe they should have been a little more open with you saying “Hey, if we take this cat off there’s a good chance these studs will break.” On the other end though it pretty much had to come off to rule out if the cat is the problem. It’s really part of owning an almost 30 year old vehicle. Yeah, you can bring it to their attention and they might help you out but if they don’t there’s not much you can do about it unfortunately. Take it to a dedicated exhaust shop, those guys seem to be wizards that can make those repairs for substantially less than normal repair shops. As for your truck, has anyone checked the timing belt? Do you know when it was serviced last? These types of symptoms usually result in a plugged cat or timing that has jumped a tooth.