I had something similar.
Motor would splutter and die above 5000.
Worse when the motor was warm.
I could get above 5000 if I got there slowly but if I buried my foot in the carpet it would splutter at 5000 then back fire and cut out.
When I backed off it would be Ok.
Bought a new mallory mechanical fuel pump (which looked pretty much the same as the one already
fitted) - problem solved.
I replaced the distributor cap leads and plugs first - but this made no difference.
The pump was about 50 dollars US.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.