The fact that test sheets print OK but documents don't suggests a driver problem; however, the fact that it's the same with two computers tends to discount that.
If it prints a nozzle check pattern OK, with no lines missing, it doesn't sound like a cartridge problem. Despite that, it may be worth running the print head alignment routine again, manually if necessary.
Incidentally, for future reference, you don't need to do a print head alignment when you fit new ink cartridges - it's only required if you have a printing problem or when you install a new print head.
Not really helped much, have I?
The plural of "anecdote" is not "data".