98 misses under load

I have a 95 Regency 98 with a 3800 in it. It runs fine under idle, and at speed. However, under load (accelerating and climbing hills) it develops a miss and will occasionally backfire. It seems to run fine under cruise control. The problem also seems to be intermittent, happening more frequently when the weather is warm or after the engine has warmed up on a cold day. I have replaced the fuel filter, coil packs, plugs & wires. Anybody have any ideas what to check next?

Welcome to AF. Was this there before the work was done? Any check engine lite issues?

The changes were my steps to attempt to rectify the problem. It hasn't altered the symptoms at all. No check engine lights have appeared.

try getting the computer checked for codes. however it does sound to me like a valve is burned, or even a a timing issue. this would account for the backfire.

Timing issues and Burnt valves are extremely rare on a Series II L36...

I would also have the codes checked... Keep in mind that this car has an OBD2 connector under the steering column, But this is an OBD1 compliant car... You will need either a dealership or shop with a Scantool that will read the OBD1 Protocall with the OBD2 cable.... Even an Actron CP9145 or CP9150 Tool with the OBD2 cable will read the 95's...

I'm interested to see if you have any handshake codes