Hi Willy.......the first thing you need to have done is a Code Scan. As soon as that CEL came on the first time, codes identifying the problem system or electronic component would have been stored for diagnostics.

Also, you said you were accelerating up a steep grade. The 98 E300 has a ASR traction system. If it detects any slip in the rear tires it will limit the RPM until traction is regained. Basically it will put the car in limp mode and no matter how far you depress the pedal the ASR overrides the imput until the tires have a grip. Also make sure you have the rocker mode switch on the console set to "S" and not "W". "W" is for Winter driving and skips you into 2nd gear so the tires don't spin on a slippery surface when starting off. Being set in "W" on a dry road would give you a feel of being sluggish.

But do Scan for the codes to see what is going on!

__________________
FRED

Daily Driver: 98 E300TD 199K
Hobby Car: 69 Austin Mini
Past Diesels: 84 300SD, 312K
87 300SDL, 251K
94 Chev. K-1500 6.5Ltr.TD, 373K