Minor power loss when hot?

'88 4.0 runs well, 156k on it, no vacuum leaks, no other problems right now, brand new exhaust manifold, magnaflow cat, and new stock muffler.

In the morning (~65-70 degrees F) it seems to run/pull stronger on the freeway than on the way home (after sitting in 90F all day). It is a noticeable difference. It'll run slightly hotter on the gauge on the way home too- yet still under 210.

There is no sputtering, hesitating, weird idle, etc- just seems to lack a little power when hot. It doesn't start any harder or easier hot or cold (always takes a couple seconds, but I think that is a Renix thing).

Anyone know what could cause this? Is it just the cooler air giving me more power (a la cold-air-intake)? I was under the impression that XJ's like to run hotter (~210) and that cold-air-intakes don't add much power at all.

Thanks for any

Three words for you--Cold Air Intake.

I would grab an intake tube from Rusty's, add the filter of your choice, and bend up some aluminum to make the shield.

Pretty much a DIY project, no one makes a cold intake kit for the Renix.