Transmission is shifting hard and late out of first gear if left in drive.

If I start from second gear it shift into third fine, and the same even if I leave it in drive and it starts from first.

There is a fairly constant leak of the ATF due to the pan gasket needing to be replaced so could this be just an issue of the ATF being low or more of a transmission problem?

It only recently started doing it...

 

Thats classic for this transmission. Did you pull any codes from the computer? P-1870 for example?? More than likely what you have going on, and its very common in this transmission is a worn TCC regulator valve in the valve body. This is a pressure regulator valve which commonly wears out its bore in the valve body which results in ATF leaking by the worn valve and reducing hydraulic pressure in the converter clutch. The converter clutch starts to slip, sets the P-1870 and maxes out line pressure in the transmission. Thats why the harsh 1-2. What I do with these is get a new valve and sleeve kit from a company called Sonnax. I remove both the TCC regulator and isolator valve trains, ream the bores and install the new sleeves and valves. If the converter is still good you're set. With the number of miles you have, its probably worth it to rebuild it and do the valve job on the trans at the same time.