C36 stumbing/hesitation on acceleration

[ke6dcj]

Our 1988 300TE with a 1995 C36 engine (AMG'd M104) is experiencing a stumbling/hesitation on acceleration between 2800-3200 RPM. It also doesn't feel as powerful at the higher-RPMS.
This is a hybrid car. Think of it as a 1995 E320 W124 wagon with a C36 engine, computer, and tranny.

The car had all filters (air, gas, PS, self-levelling) & fluids (oil, ATF, diff, PS, self-levelling, brake) changed about 3K miles ago. Plugs & plug wires were changed 10K miles ago.

The car starts right up, no problem, and it feels like the entire engine is stubling/hesistating to accelerate.

No "CHECK ENGINE" light (OFF).

What's the proper diagnostic procedure?

Do I need to get the Mercedes HHT connected to read-off some codes?

It happenned 2-days & 80-miles after my last fill-up (ARCO Premium). Should I change out the fuel-filter?

The car has been in the rain for the last 5-days (we're remodeling). Should I check some connectors and clean them up?

Thanks in advance and Happy New Year!

:-) neil
1988 360TE AMG
1993 500E