I had a local shop read my DTCs and there was a 19 and a 26 stored.

I read the 19 has something to do with injectors and the 26 has something to do with an upshift delay relay in the transmission.

How do I troubleshoot further?
The codes were reset and the CE light went off for about 10 miles and it came back on.
The engine runs perfectly...the transmission shifts a little hard and is slow to engage reverse...but nothing terrible.

Thanks for any advice as to my next step.

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1995 E300 Diesel
1994 E320
1999 C230K
1994 S500 W140
1990 300 SEL