Hesitation

94 Transport 3.1
New Engine Installed close to 100k miles on it..
Runs smooth but.....

When I turn the ignition key it...

Hesitates for a second (Hope I'm saying it right-maybe slow crank is better) then starts
It doesn't stall after this but...
When I give just a little gas like I am pulling out the driveway it hesitates when I depress the gas pedal like it will stall then gives me power...

I thought that because the mechanic used 20/50 oil on the engine install it is doing this..Any thoughts? Thank you....

Nothing to do with oil unless you are at the south pole..
FUel is delivered on this engine according to manifold pressure, engine coolant temperature, throttle position / rate of change of position. Any one of those
sensors can cause hesitation when depressing the gas pedal.
However, slow initial cranking - battery and starter being OK - might indicate too much advance on timing, which "might" also influence throttle response at slow speed. SInce this one has a rotary distributor, I'd check this first as this is really easy. Retard timing a little just to see. Easy things first.

Nothing to do with oil unless you are at the south pole..
FUel is delivered on this engine according to manifold pressure, engine coolant temperature, throttle position / rate of change of position. Any one of those
sensors can cause hesitation when depressing the gas pedal.
However, slow initial cranking - battery and starter being OK - might indicate too much advance on timing, which "might" also influence throttle response at slow speed. SInce this one has a rotary distributor, I'd check this first as this is really easy. Retard timing a little just to see. Easy things first.

Like the south pole ref...he he

Turns out the alternator is suspect..

My battery was running way low this morning...()In the red) Replaced with a new one so the ABS light, Slow crank disapeared...But still slight hesitation at times when I gave it gas...
Note...the new alternator was put in at the time of engine install, so I don't understand why I could not hold charge...
New Battery is now running low..What gives???! Bad Alternator?
Thanks

Well...a good battery is the first easiest thing: glad it cranks.
If you had a good alternator on previous engine, better get it back. Those alternators are POS. ...more later......

What about a oil leak; it appears to be two inches to the right of the starter solenoid thin bead of smoke when engine is hot. Can it be repaired?

OK...check voltage with engine running: should read around 14 volts..does not matter if 14.1 or 14.5 or even 13.9 (mmm... little low) as long as well above 12.6. If 13.2 -13.4, you may have a busted diode. 12.6 or lower, regulator is out. If can't get your old one, a diode block (get a Bosch - the Delco original is a scrap - ) is like 25$, same $ for a regulator. I changed both on mine, a year in between.
Hesitation....cold only or even when warmed up?

Hesitation greatest on cold...when warm it was slight but noticable, backfired once or twice as well