^^If you convert the 3 mil into USD in Thailand and carry to Singapore you will be required to file a Physical Currency and Bearer Negotiable Instruments Report (Traveller) or NP727 form when entering.
Personally I would avoid carrying some 100k USD in cash with me pretty much anywhere, much less on a plane into Singapore.
Just go to your bank and tell them to wire the money as USD into you Sing bank account.
According to Bangkok Bank you will need the following information to make the transfer out:
To transfer funds overseas you will need the following information:


- The recipient’s account name, account number and address
- The name and address of the recipient’s bank
- The SWIFT address of the bank that they have an account with (if any)
- Supporting document (Thai citizens – A document stating the purpose of the fund transfer; Foreigners - A document stating the source of the income).
As it appears you will be using the money in Malaysia, it seems to me you are going to lose whatever gains you make on the THB-USD conversion (minus comission and transfer fees) when you convert to MYR (minus commision again and transfer fee again).
If you are truely leaving Thailand forever, I would just send to Malaysia once, but that is just me.
TH