1997 Toyota 4 Runner truck had lost some power

1997 Toyota 4 Runner mileage 185,000. I noticed that the truck had lost some power, so I changed the plugs, wires, air filter and fuel filter. The truck is super responsive and revs up clean, definitely a noticeable difference. I also had the timing belt done back at the recommended 90,000 or whatever it was; not sure off hand but it is about due for another timing belt. Anyway it pulls strong, but seems to have some very minor break down on the top end at about 4500 rpm or so. It is faint, but as I build and race cars (Camaro's) I notice it. You can hear the motor rev and it does accelerate but not as strong as it should, almost sounds as if it is bogging a little, but seems to be more of a breaking down (loss of spark) than anything else. I am thinking it is coil related? The truck has three coil packs one fires one plug on one bank as well as the other on the other bank. The truck is completely drivable, does not have any skips or misses, however seems to have some break down as mentioned. Any thoughts are greatly appreciated. I drive the truck pretty easy, but noticed the problem when accelerating onto the highway. The car does not pull any codes.