2005 Mazda MPV Uneven Acceleration

Ok, I'm gonna be as detailed as possible for ya.
Bought our 05 MPV used with approximately 72k and she ran just great. We are sitting just over 84k and there is this ongoing issue that I've yet to fix.
The uneven acceleration is evident at both start up and throughout any short or long drive. Any spirited acceleration, under load, will usually result in a "lumpy" or uneven gathering of speed. It hasn't affected our mileage- I still average just under 20 mpg with a mix of urban and rural driving. I've replaced all 6 of the COPs along with the spark plugs(OEM) and also the PVC hose and valve that are very prone to failure. I've replaced the air filter with a K&N and cleaned throttle body and the MAF and IAC sensors. The transmission fluid was changed as a last ditch hail mary- no dice however.
When I replaced the COPs and the spark plugs the upper intake manifold had to be removed, so I changed out the gaskets for the upper plenum, throttle body, EGR valve and IAC. What gives? I must be missing something- but it isn't throwing any codes I can reference for you guys. I know you'll mention vacuum leaks- and if you think it's still the case I'd like a tip or two on detecting them- the throttle body cleaner around all the vacuum related parts while the engine is idling and listening for errant sucking sounds or a surging idle isn't doing the trick. Thanks for your time and expertise!