Hardenuff

Hi everyone,
So my car is a 1973 280sel 4.5 with a new pentronix electronic ignition removing the points and I recently posted asking about timing.
Well another issue I have which may be related is how it accelerates.
First of all when I start it up in the morning, and let it warm up, it starts surging (for lack of a better term). The idle revs up and down for some reason.
Then once it’s warm and i get in to drive it, the car will not go faster than about 40mph most of the time though On rare occasions it runs descent and can do 70mph.
But all of the time, the car has never let me floor it and get anything other than it choking. It seems as though once the gas pedal reaches a certain point it’s getting too much gas, not enough gas, or has a bad air/fuel mixture....all amounting to it running like S&i@!
Can someone help me with some answers?
Embarrassing is an understatement when u r in a beautiful car on the freeway doing 30mph on flat highway or 15mph going up hill.
Sorry for the novel but I wanted to explain in detail.