2001 f250 4wd taking off in 2nd gear, not 1st

[kystanger]

I bought a 01 4wd 7.3 f250 with a 4r100, I got it cheap because of tranny problems just thought I'd ask about it. When I bought it, it acted like it was low on fluid you had to rev it up a bit to engage. I pulled the pan and the filter was loose. I installed a new filter and changed fluid, now it engages perfect and pulls but is taking off in 2nd and not 1st. If you pull the shifter into low it acts like it takes off in 1st. Any thoughts before I tear into this thing. Thanks