'02 ram 3.7L issues

working on a ram 3.7 with 120,000 miles on it, has a bad misfire and pocket scanner gave me a p0306 code (#6 cyl. misfire) . replaced plugs and coil but still no remedy. checked compression and gave me a low reading compared to the other 5 cylinders. they read at 150 psi and the #6 read at 80-90 psi.
anybody else have this problem? and will i have to replace the piston rings at my cost or is there a TSB or recall or something about this.
this truck has low miles IMO for this to happen.any help or advice

Is there exhaust smoke?

it is most likely not the rings, but is probable a burnt valve. was the truck "short tripped" and did the owner use cheap gas with the epa minimum detergent?