HT4100 Bog Cause?
 

I’ve had many 4.1 Lter Caddies and most but not all have the bog as I call it. They idle good, throw no codes, but once you depress the accelerator they kinda push back before moving forward, like their fighting for fuel. I’ve done many things thru the years but nothing seems to get them as they were when new with responsive acceleration. Any ideas? Experiences? Thx!

1983 Fleetwood with 27k miles
1978 Seville with 31k miles