New to the forum, searched and found the threads about coil issues and transmission issues, mainly the possibility of a bad torque converter. However, I don't think I have either issue, although my symptoms are similar.

1) Under WOT, only between 3 and 4k RPM's, the RPM's bounce and engine surges. It runs so poorly the engine has trouble accelerating out of this RPM range. Once out of 4k(ish) RPM's engine pulls and runs great. Under about 3k RPM's the truck runs fine. Engine runs fine in all other throttle positions besides WOT.

2) The truck idles fine, but sometimes it seems to idle maybe a little rough

3) In O/D, between 45 and 55 MPH, mainly when going up a slight grade in the road or when accelerating slowly, the truck "bucks" or "jumps." Once I turn off OD or I apply enough gas for it to shift down, the problem leaves.
In one situation, when I had 5 passengers in the truck, I was going up a slight grade in the road and it started bucking... I applied some throttle to make it shift out of OD, however, it did not shift down in a timely manner. In fact, the truck lost about 4 MPH on the speedo before it shifted down. This time, it almost seemed as if the tranny was stuck in OD and could not shift out.
This makes me think torque converter, but with the other symptoms, it seems like a bad coil may be the culprit.

4) Engine has classic phaser tick, but more severe than most. Also, it sounds as if I have a loose timing chain. It sounds like it is slapping the plastic guides.

5) Cold starting in the morning of winter months seems to require more cranks than it should.

I took the truck to my mechanic and he hooked it up to his diagnostic software and we drove the truck. His computer picked up no misfires.

My mechanic recommends servicing the tranny. I am hesitant because he seems to be ignoring the WOT acceleration issues and seems too quick to jump to a bad TC.

I am also hesitant to service the transmission because the truck (2004) has 108,500k miles and has never had the transmission serviced. When I bought the truck, with 105k, I was aware of the lack of tranny maintenance but planned to flush the tranny soon. I did not know flushing after a missed interval has a high chance of causing further complications.

So, I am needing some advice. I am a college student and my funds are limited. If money were no issue, I would probably change all plugs, wires, and coils first, but I hate to spend that money if it doesn't fix the issue only to realize it is a bad tranny. Where should I start? Fix the phaser and timing chain? Replace coils? Service tranny? Possibility of bad injector? BTW, engine is the 5.4.