94 F150,2wd,5.0 with MAF. Trans code U. 3.55 gears.
Trans fluid is good,was recently changed with a fresh filter installed and torque convertor drained at the same time.
Shifts hard into 2nd,seems worse when the truck is warmed up.
The rest of the shifts,2nd to 3rd,and into overdrive and torque convertor lock up are all fine and normal,shifts into reverse with no issues.
What is the most common issue and first thing to check?

 

I believe you have the E4OD transmission. Mine did the exact same thing. I had the solenoids checked, fluid changed and nothing helped. Turned out the sprag gear for first was damaged. $1500 later and a fresh rebuild with upgrades and she shifts likes a new truck.