2003 Dakota 4.7L V8 with about 42,xxx original miles on it, automatic trans. Bought about six months ago with about 39,xxx miles on it, so I don't have the full history. Daily driver, only about 4 miles each way to work of highway/backroads combined.

Issues:

1. 1st gear will not shift until at least 11-12mph (can't tell if this is just the normal first gear shifting ratio or what)
2. Around 30-40mph, under moderate acceleration, engine RPMS just keep going and going until it finally shifts - doesn't seem smooth anymore and feel like it should be shifting much sooner
3. Biggest new 'issue' is at cruising speed on highway (around 50-60mph) regular rpms sit around 1,500. When I go to lightly/moderately lightly accelerate for passing, rpms blip up to 2,000 and immediately back down to 1,500. To get any sort of acceleration I really need to depress pedal (almost to floor) to get any sort of downshift. When downshift finally occurs, it feels like it is downshifting two gears and rpms jump up to over 3,000
4. Something is absolutely robbing gas mileage - never going to win any mpg awards but almost overnight my mileage is way less, for no apparent reason

Just had transmission checked out and got clean bill of health from two transmission specialists. I would have sworn that these issues were transmission related but they said they cannot find anything that would lead them to believe it's the transmission. They checked the computer too and said it wasn't throwing any codes. They mentioned it might be some sort of engine misfire that's causing a loss of power.

Any thoughts here?

UPDATE: got the exhaust and catalytic converter tested at an exhaust shop yesterday. All back pressure and everything is within the right range. They didn't see any clog or problem with this part of the truck.