High-ish RPM while in park but not while in gear? Normal or concern?

My 2002 seems to have a slightly high idle while in Park only and mostly after cold starts. It's at about 1500-1750. I can let it warm up for up to 10 minutes after cold start, well after the engine is at operating temps and the RPM doesn't go down. I'm newish to this truck so that might be normal. If so please chime in.

The truck turns over, starts and like normal the RPMs decrease after a few seconds, however it never seems to rest below 1500 unless it's been driven around for awhile. After the engine has warmed up to operating temps and it has been driven, the RPMs are around 1k while in park. This happens with or without AC/heat turned on.

This might be a stupid concern, as for all I know it could be very normal but the truck is very new to me and certainly has its oddities at 260k miles. This is the 3.4L engine.

It does have a CEL on (P1135) for 02 sensor, which I haven't got around to yet. This might have something to do with it.

 

The p1135 code will adjust fuel trims and will most likely be the cause of the high idle.

 

Check the vacuum line to the dashpot on the lower passenger/firewall facing side of the throttlebody. This dashpot can make the truck idle up continuously.

 

Update: The issue has fixed itself. I forgot I was messing with the O2 sensor mentioned in post. I unplugged it and plugged it back in to ensure it was connected properly. The engine was re-tuning itself after a few drives. No longer have the RPM issue any longer!