2005 Chrysler Town and Country: engine is little choking once started

I recently bought this van with only 100K miles second hand (meaning from the
previous owner, not from the dealership).He was an older guy, probably didn't really
had time to keep the vehicle up to service schedule.
I took it straight away to Tire Kingdom for tune up. As usually they all do, starting
fooling me that vehicle requires lots of replacement parts, some unique, special fuel
cleaning procedure, alignment, belts, shock / struts  and so on. I picked up only
needed procedures: simple fuel system cleaning, oil change and alignment, which
totally cost me around $500.  
However, shortly after I noticed some symptoms that I would like to see if someone
else experienced the same:

1. Roughly getting 15 miles per gallon in the mixed driving type (40% - highway, 60% -
city). With Track off and AC off can go up to 17-19 miles per gallon.
2. Accelerating gas pedal doesn't lead to any vehicle boost. Car feels like a pregnant
cow that just about to deliver a calf. Very slowly increasing speed. I replaced an air
filter, but that didn't help
3.If gas tank if filled in full, for the first 1-2 minutes engine is shutting down and feels
like choking. I have to press and the gas pedal little bit and keep the rmps at around
2K.
4. There are absolutely no check engine light on the dashboard, but I feel that vehicle
is not healthy. Can't it be that previous owner or other owners just simply unplugged
the cable?

I understand that all aforementioned symptoms may be a signal of different problems,
but something telling me that this might lead to one of the possible solutions:
-either fuel filter / fuel pump is bad
-either some sensor is bad (not sure which one exactly).           


Thanks for your advises guys!