• The 4l80e tranny is usually bulletproof but there is the odd bad unit. Do you hear any noises while driving that weren't there before? (aside from the *clunk* of a tough shift) Is this the first time you've serviced the tranny? How many kms on the truck? The hard shifting can be attributed to neglect, but the slipping out of overdrive may signal an internal gear problem where they are not engaging properly. You may need to take this into a transmission shop for an inspection.

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