2000 bravada engine issues

[nascar20]

138k miles, all maintainences, is rough starting, poor idle and dies. Knocking noise at top end until over 1500 rpm then quiet and runs strong. poor acceleration until 1500 even after warm. New plugs and cap and rotor. Found it low on oil after oil change 4 weeks ago. Was filled correctly at oil change. inspectionm and working on it today same things after new parts. removed oil cap while running and is puffing smoke like a train out the oil fill, once it is revved over 1500 it goes away and never smokes again until let off gas. Got a code reader and found cyl 4 misfire. Drove truck 20 miels and misfire went away to the point the computer cleared the pending code. Ran great, almost no miss or noise. shut it off and restarted and it missed and made noise. so I left it at a shop and he just called me and said cyl 4 misfire, has a little compression. The valves are ok cause he said it had vacuum. says it needs a motor, probably broken ring or hole in piston but probably ring cause it has a little compression. I just don't believe it needs a motor or that something is not causing this other than a bad cyl. It just started overnight with no tell tale signs and there has to be something else to do to it.

[Chris Stewart]

What does #4 spark plug look like?
138K is kinda soon to have piston slap & loss of ring & compression control but idling in traffic with the AC on in hot weather can create a terrible environment for soft metal like pistons and bearings.
You might try a heavier oil like 20W-50 Valvoline just for kicks but it'll have to be replaced with 10W-30 when morning temperatures get back down to the 40's to avoid building too much oil pressure.