Is this normal for a 5-speed? What might cause this. It's still under warranty but I don't want to appear as a total doofus to the service manager. I have only 25k on the truck. I don't think it's the cooler weather becasue it shifted fine last winter. I switched to Mobil1 synthetic ATF at 20k. Thanks in advance.

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1999 XLT SC, bright red, 4.2l, 5 speed, MAAP stainless nerfs, Prime Designs bug deflector, Astro Euro-Lid II, Mobil 1 Synthetic Oil and Transmission Fluid.