Possible ground issue , check your wiring very closely tugging on the wires at the connections. Replace the rubber vacuum lines . Sometimes they look fine but when they get old they can collapse with vacuum applied . Also check your EGR valve , could be clogged .

 

I had the same thing happen to me a few years ago at 180,000, it was the fuel filter.
The filter restricted the flow under high use/speed.
Filters are cheep and easy to replace.

Hope this helps,

OD45

 

I had a clogged cat and it was doing the same thing.