My truck (5.3 Hemi 28k miles) seems to not always want to shift into the next gear when I’m going around 30-35 mph…it stays at about 2k RPM, too high. Other times it will shift smooth and run a little over 1k RPM. When it doesn’t shift and is at 2k RPM, if I “tap” the gas and let off it, the truck will rev up to 4K RPM then come back down to 2K RPM, and finally shift and go to just over 1k RPM, where it should be. What’s going on?