I've seen cars like yours. What country are you in? I've NEVER seen an SL with a S/E switch on the shifter. Yours must be EURO Specification. Shifting hard could be various things. One simple thing is when was the transmission serviced (filter/fluid)? Remember the vacuum modulator controls how hard the transmission shifts. I'd adjust the modulator key counter-clockwise to see if shifts soften.

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Only diesels in this driveway.
2005 E320 CDI 243k Black/Black
2008 Chevy 3500HD Duramax 340k
2004 Chevy 2500HD Duramax 220k