i had the exact same codes, i used my scanner to check and erase them and within minutes it comes back, so i replaced the round vaccum unit and the that cleared
the p0401. but the p0770 seems to be not wanted to go away, so i went and drained the tranny, removed the pan and checked out the firtst solenoid pertaining to
p0770 code, wiring connector seemed pretty tight, it was difficult to take it out to replace, because other items were blocking its sight. so i replaced gasket,
filled tranny and erased the code and it came back. but then, i did got to have a smog check done and failed, the p0770 code and problems with the oxygen sensor.
funny thing is i put in a new oxy sensor and erased the codes, passed smog.. and behold no check engine light, drove it for about 500 miles with no light, but then
the light came back, check it again same code p0770. so i gave up for now.. since it runs fine.