It could be an ignition problem. Failing coils sometimes work OK at low rpm and light load but break down at higher rpm and higher load but anything else in the high voltage side can do it - distributor cap, rotor, plug wires, plugs.
85 GTV6 3L
76 Suzuki GT500
2011 Jaguar XKR
A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke