Help! Lender says DTI is too high.

[JaNae Anderson]

Frustrated. My situation is a little complicated but i'll try to provide as much detailed information as possible. I'm looking to purchase a off the market duplex for $400k. Each unit can potentially rent for $1,600-$1,700 a month. The down payment will come from my husbands inheritance as a gift but I've been informed by my lender that gift funds can't be used on investment property. I understand that but one of my many questions is will it still count as a gift if my husband has the inherited funds wired to our joint account? My husband is not a option to go on the loan with me. I have a primary home that will turn into a rental property Jan 1st 2018. The monthly PITI for the soon to be rental $1435. My pretax take home without using the future rent in January is $4,300. I currently have a car note of $600 but it will be paid off Dec 15th 2018. The only monthly obligations i'll have after Dec 15th is my primary home that's turning into a rental property. Here's the part I don't understand. If I'm able to use 75% of the rent towards my income and we plan on putting down $150-$200k on the duplex, how could my DTI still be too high to qualify for the duplex?

Here's some numbers: 

Take home pretax income is $4,300.

Rent income from 1st rental $1,650 , (PITI) $1,435 

Using the lower potential rent income for the duplex will be $2,400,  If we put down $200k on the duplex the monthly PITI will be approx $1488.

Please let me know if I'm calculating properly but going off these numbers my DTI looks like it would be below 37%.

Here are the questions i have 

Do i have too many contingencies that's causing the lender to say that my DTI will be too high? Meaning that all the rents will have to applied in order to qualify.

How soon can the rents be applied?

If we wire the funds from my husband into our joint account, will the funds still have to season? 

Please let me know if I'm leaving something out.