My sons 98 camaro V6 auto with tune up 5k ago just started missing when in overdrive going up steep interstate or highway hills. If you downshift it stops. Any ideas on where to start? Water in a fillup Maybe? Appreciate any suggestions. Bye the way it has 85k miles but barely uses half quart every 3k miles.

Sounds like a fuel filter.

Make sure you are not confusing lugging the engine with it missing... Both will chug burp and fart a lot alike.

try tapping the brake pedal when it happens- that should unlock the torque converter and might get it to stop doing it.

I thought fuel filter too but it was changed 5k ago. Still wonder about moisture in fuel?

You may have a transmission problem if it doesn't downshift out of overdrive when going up a hill...

yeah
like a vacum leak on the modulator line

GM hasn't put a modulator on any of their trannies since they quit using the TH400 about a decade and a half ago in full size trucks. they either have a tv cable or- if it's newer than about 93 or so- went totally electronic.

when was the last time it got a fluid and filter change? even if it aint the problem, it can't hurt.

You can plug a fuel filter with 1 bad tank of gas. Change it and dump in some fuel line deicer to help remove water from the fuel system.

first off is the check engine light on? the 6 banger cars are bad about coil packs, wires and modules for missing. i know this because i am a auto tec i repace about 40 coils a year on theses cars, if u plug a snapon scanner in it will tell you what cylinder is missfireing

noct (huh ?)
In OD on a hill puts the most load on the engine and the ignition system. If it has not had a good tune up in a while, it will probably help. You might want to start it at night and have someone "power brake" it while yo look at the plug wires. My guess is that a few of them will be arcing. Plugs will do the same thing. Might be worth having someone put it on a scope so yoou dont waste a lot of money throwing parts at it.

Miss under load sounds like an ignition wire breaking down. imo

Stop going up hills in overdrive............sorry could not help it. I would be looking at the ignition system also. MIght also want to look at the TPS or throttle position sensor.

Try power breaking the motor at night. Set the brake so as not to mame your helper who looks for sparklies under the hood.