Dodge: help, transmission fluid change, oxygen sensor

Question
Hi
I have ford E-150 1995, 5.0 L V-8 170,000 miles
I did tune up on this van few days ago:
-oil change, filter change
-transmission fluid change and filter
-power train fluid replacement
-oxygen sensor change
-spark plugs
-spark plugs wires
-ignition coil
-fuel system cleaner, transmission treatment, and oil treatment added
After two days of driving (there was no problem before) my truck just starts dying.  After few miles on the highway or anywhere it slows down and when you press execrator nothing happens.  You can press it even to the end and van will go 25 miles/h. In the same time truck starts firing, there are spaces between ignition and sometimes it just dies and engine light goes on.
I don't know what to do. Van works great for few first miles. Gears work great and there is no problem.  Then when everything is hot something doesn't work.
Please help me, i was thinking about taking the gas tank out and checking it, or fuel evaporator  
wojtek

Answer
Iwould connect a codescanner to this one from a cold start.
This "sometimes" problem can be very difficult to detect.
I would examine the scanner as engine temp reaches the
190f level. Also note all voltage parameters during
operation of the van. need help call 9126534401.