Toyota Repair: 4runner transmission problem, head gaskets, problem background

Question
Background-2wd 4runner, 3.0, automatic had head gaskets replaced and ended up with trans problems.  When you put the truck in D it starts out in 3rd.  If you put it in L it starts out in 1st.  You can shift from 1st to 3rd by going to D and the overdrive is working.  It never has 2nd and the OD light flashes constantly when in OD.  I don't know where to start other than a Toyota dealer.
Appreciate any help.

Answer
Since the O/D light is flashing I would recommend having the trouble codes in the transmission computer diagnosed first, since this happened after the headgasket replacement I really don't think that the transmission has a problem, think that some electrical connector may not have been reconnected in the process of replacing the headgaskets.