[DML] Need some insight or guidance for locating problem

[dstall@xxxx]

Earlier I posted a note about State Farm insurance and also a problem
about my DMC-12 automatic lugging down as if there was a fuel problem.
The problem: I'm driving along and the car slows down as though it is
running out of gas; if you turn off the key and then turn it on again
the car accelerates back to the speed it was running at and all is well
for about 2-4 minutes and then it repeats the slowdown again; turn off
key and turn on and its ok for a short time again.

What I've done. Replaced fuel pump relay; replaced fuel pump, gas
pickup line and filter on fuel pump inlet. 
Diagnostic setup: 
1. put tap into fuel line at fuel inlet on fuel distributor with
pressure gage 2. put 12 v light on power line going to fuel pump in
fuel pump relay with other end of light grounded. 
Observations:
1. The fuel pressure is at 75-80 psi while engine is running and about
45-50 psi at rest. 
2. Light is off until car turns over to start and then it stays on and
doesn't go off when car slows or until key is turned off to quit
3. fuel pressure doesn't waver at all while car is running or slowing
down. 
4. car has good acceleration and power except when it slow as if fuel
is starving; also I hear something that sound like preignition knock on
occassion when it is slowing down with throttle depressed. 

I'd like thoughts on what to check out next. Insight or suggestions
will be really appreciated.

DaveS
dstall@xxxx