I believe what the OP is asking is what his adjusted interest rate is after considering the additional refund he would receive from his tax return. Here's a very simplified formula you can use on a year-to-year basis:
INT = Interest paid on the house that year [$7,379.61]
PT = Property Taxes paid [3,000]
IT = Income Taxes Paid [$2,500 estimated]
OD = Other Deductions you have listed
SD = Standard Deduction [$9,700 for 2004 married joint filing]
TB = Taxes Bracket rate [15%]
AP = Average Principal over the course of the year [calculated below]
{ (INT) - { [ (INT) + (PT) + (IT) + (OD) - (SD) ] * (TB) } } / (AP)
So, in your example, we'll estimate you had $2,500 income tax you could itemize, and no other deductions.
{ $7,379.61 - { [ $7,379.61 + $3,000 + $2,500 + 0 - $9,700 ] * 0.15 } } / { $135,000 - [$135,000 - $133,181] / 2 }
{ $7,379.61 - { $3,179.61 * 0.15 } } / { $135,000 - $909.50 }
{ $7,379.61 - $476.9415 } / $134,090.50
0.051478 = 5.1478%
As you can see from the second last line, the formula is simply the amount of interest you actually paid minus the difference in the refund amount you would have received if you didn't have the house, all divided by the average principal over the course of the year.
If you eliminate the refund amount, the $7,379.61 / $134,090.50 should come out to be the actual interest rate of your loan.
Hope this helps.