High idle and stuck in first gear, automatic transmission

[Hoserdave]

This has been intermitted problem. I changed transmission fluid. the truck will stay in first gear unless I shift it down in two second, automatic transmission. If I shift it into neutral, the idle goes up to about 2000 RPM. no engine lights on the dash? should I change or clean the IAC part. or and change the transmission solenoid? both of these happen at the same time. 2001 Ford F150 5.4 LHelp someone please