'To' followed by Gerund or Infinitive

Hi,

I'm confused about when should we use a gerund after 'to', I know that if 'to' is a preposition, then it must either be followed by a gerund or noun, the thing is, I cannot differentiate whether 'to' is a preposition or part of a to-infinitive.

One suggestion was:

"It is possible to check whether 'to' is a preposition or part of a to-infinitive: if you can put a noun or the pronoun 'it' after it, then it is a preposition and must be followed by a gerund:

I am accustomed to it (the cold).
I am accustomed to being cold."

But I don't know whether or not this suggestion holds true, as I came across some other sentences that I can put a 'noun' or 'pronoun' after 'to', but sometimes the author used infinitive.

Examples:
i. Start by committing to (*measure/ measuring) your life based on...
ii. I have agreed to (*give/ giving) you a car.
iii. I give priority to (do/ *doing) it.
iv. The secret to (get/ *getting) everything you want.
v. I object to (work/ *working) overtime.
vi. The kind of person you're committed to (become/ *becoming)

The words with asteriks are according to the original articles. I feel that I can put an 'it' after 'to' for the examples above, sounds a bit weird to me for number vi if I do so. But examples i and ii are given as to-infinitive.

The first example seems inappropriate to convert 'measure your life based on...' to a noun phrase, so I think it's okay, but the second one I think I can put it as 'I have agreed to "your proposal"' where your proposal is 'giving you a car', but the actual sentence was written otherwise.

For examples i and vi, both are 'commit to', can I use 'become' instead of 'becoming' for vi?

Please enlighten me. Thanks a lot.

Troy, as confused as he can be...