2002 5.9 w/ 115,000 Durango 4WD
Tick coming from cyl 1 after warmup when you let off the gas driving down the road. Oil Pressure drops to minimum after thermostat opens from straight up at cold start

Pulled the valve cover, nothing wrong with the rockers or lifter.
good oil flow, nothing loose. new plugs, no problem with other 7 cyl
gapped properly

Next to check is the timing chain.

Other ideas?

 

If its an isolated tick to only Cylinder #1 I'd check the injector for proper flow as that's most likely it.

Oil pressure dropping once thermostat opens... How old is the oil? Could be that its older oil and it's viscosity is getting thrown off from what the vehicle is used to. What weight oil are you using and how much mileage is on it?