Could I use mercon V ?

Mercon V is backwards compatible and can be used in place of Mercon. There is an alternative which is called Valvoline Dex/Merc which can be used in place of either of the original Dexron III or Mercon products

Beginning immediately all automatic transmission / transaxle applications requiring MERCON(R) can now be serviced using MERCON(R) V or MERCON(R) Automatic Transmission Fluid or dual usage fluids labeled MERCON(R) / MERCON(R) V. 

You can also use it in the power steering.

My manual for my 2001 Ford F-150 (4.6L v8) says that the transmission fluid is "Mercon V". For power steering fluid it lists "Mercon". I can't even find something on the shelf listed as "Mercon". I've got several quarts of "Mercon V" leftover from a transmission fluid change

Mercon LV is a low viscosity synthetic ATF where as Mercon V is a universal synthetic ATF. I believe LV is recommended for transmissions 09+ and is typically advertised as fuel efficient. For your power steering you're going to want the Mercon V.

Motorcraft MERCON V is suitable for use as a hydraulic oil in a wide variety of industrial applications that call for an ISO 46 or SAE 20W viscosity grade hydraulic oil. Motorcraft MERCON V is a premium-quality automatic transmission fluid.