In OP's context, uprooting is a gerund - a verb form functioning as a noun (so in this case, it denotes the action of "to uproot").
Although uprooting can be used transitively (so it can take an object, such as plants, or your life here), this doesn't change the fact that syntactically, the gerund uprooting is a singular noun. If we take a slightly different example we see that sometimes it's possible to use a pluralised -ing form (but I suspect the -ings forms are probably not gerunds, since they can't be used with a direct object)...
1: Beating children is barbaric
2: Beating the Prince is barbaric
3: Beating is barbaric
4: Beatings are barbaric
5: * Beatings children are barbaric (not valid English)
From this it should be clear that regardless of whether a direct object (children, the Prince, here) is present, and regardless of whether the object is singular or plural, the -ing form is always singular unless explicitly pluralised by appending -s.
TL;DR: The plural verb form (are) can never be valid in OP's context. The others are all syntactically valid, but mean different things. In practice, contexts where you might use past (was) or past perfect (had been) are contrived and unlikely, so if a single "best" choice must be made, the answer is is.