IR Laser gun is a great way to check for wheel and brake problems in order to narrow down where the problem is.
That said, did you ever check to see of the PB was fully releasing??
Like others pointed out, they do get stuck sometimes.
Another problem on the rubber brake hoses can be the brackets that hold them to the suspension can rust, particularly in areas that use road salts(s) and the rust swells the bracket and pushes into the soft brake line
Then the restricted line works very much like a check valve … as you apply the brakes, the hydraulic pressure easily pushes through to the caliper, but as you release the brakes, the fluid stays in the caliper, as there is no "return pressure" to push it back up the hose to the MC. The easistes way to ech for that is to loosen the clamp and see if the probem does away, though if the clamp ihas been rusty for a long time, then it might have permanently deformed the inside of the hose. Dodge Rams were readily susceptible to this problem.
