replaced brake lines, brakes worked good, took for test drive all 4 wheels locked brakes cannot find problem, truck was parked for 4 months but I've never seen 4 calipers that could be seized at the same time, is there anything else besides seized calipers that can cause this?

Are the rotors rusty?

a little bit, but it shouldn't affect calipers(all four)

Crack the bleeders and see if the brakes release. You could have a master cylinder that the piston got stuck into the bore. When you changed the brake lines did the master cylinder go dry? It could have gotten some debris down into the piston causing this issue.

UPDATE: so hated to do it but... pulled all 4 calipers, pistons sticking a bit on all 4, rear sliders seized solid, 1 broke off won't come out. sprayed pistons, but still need sliders and caliper frame. truck brakes were all replaced last year by a popular local garage, not a drop of grease in anything, this is why I do not trust garages around here and try to do my own work,( bought truck from family friends estate, was in his eighties) for son to drive as first vehicle. thanks for your help, will try to update after I get it fixed again, this garage also cut window motor cables and taped windows shut, I replaced motors after I found broken wire in door frame. 200 dollars in parts for a simple common broken wire.

on another note on this: can the pistons be pushed out and cleaned and put back in like pre 88 models or do they damage the parts trying to do that, fronts are 2 piston rear is 1 piston, the bleeders are loose so if I can clean and grease the pistons it can save atleast 400 dollars or more.