I've read many post about the fishbite/chuggle issue on the 3.8, while in lock-up, 70mph going up hills on the interstate you will feel a fishbite chuggle as if either the engine is surging or the transmission starts come out of lockup, but then does not...
I was getting this feeling..for about 6 months
everyone was posting they could never solve the fishbite feeling, most thinking, it was a solenoid, while others were tossing dollars into plugs/wires/coils/fuel filters/fuel pumps..etc
In my case, I had already done coil paks/wires/plugs, before I was feeling the fishbite
and for my car, the manifold air flow sensor was the issue and fix
it finnally sent a code for MAF low voltage...I cleaned it, with maf cleaner, but would just trip the check engine light again
so off to the parts store, I get a spectra new maf sensor..and install....but the the car would not idle, and again, cel..., I return the spectra unit, and swap out for a reman a1cardone unit, and has been working fine
I reset the computer to clear out all learned idles/driving habbits by disconnecting battery, and discharge by connecting cables together, and reconnect batt
and has been running perfect @ 29 mpg, and will pull hills effortlessly, with smooth delivery and much more power
I did a search on the specta maf that did not work, and found everyone else had the same issue, no idle, and returned part, I emailed spectra.. and they never reply
so, if your 3.8 is doing spark knock while cold, fishbite or chuggle while pulling interstate hills, boggy acceleration.. you may have a MAF sensor that is failing.
it will need to fail completly before making the check engine light to come on
amazing differance after replace