1996 Bonneville */C chugs at highway speeds. Car had new TR55 NGK plugs, new GM wires. The coil pack checks out perfect.

Car still chugs at highway speeds with torque convertor locked in 4th from 55 mph to 85mph. Chugging is fairly low frequency and irregular. I'm sure it'* not an ignition issue since we can go miles like this and no code goes up and the cat convertors are not at all clogged.

It'* probably an issue in the valvebody. Feels like torque convertor engaging and disengaging erratically.

Car is a 1996 with 156,000 miles.

Thanks

You need to get a scantool on it while you're driving it, and watch TC slip in lockup above 48mph with the cruise set on a level road. I'll bet it'* less than 10 rpm'*, which is good.

Chances are, you STILL have an ignition problem. Check the resistances of all 6 plug wires and post them here if you can.

Thanks, that'* what I'm gonna do. It'* becoming consistent enough now. Will keep people posted on this.

My 96 SE does something like that. When it shifts into OD sometimes its a little hard and it will chugg I quess, but only when im barely acc. not going over 2500 rpm'* and if I push on the gas till it shifts back down its shifts pretty hard.

I had this problem with my 97 and it drove me nuts. Finally replaced plugs with Delco platinum, and put on MSD wires and coils. No more problem. MSD stuff well worth the money. Car now has 115K, and starts quicker and runs smoother than when it had 15K.

Mike