First, I think that you might get errors when using warrtalon's formula as there are no spaces between the operations and the fields. Here is the same formula but with spaces:
(((@Ton_Estimate * @SellPrice_ton) - (@Ton_Estimate * @dsiposal_cost) + @Haul_Marg_doll) / (@Ton_Estimate * @dsiposal_cost)) + ((@Fully_Loaded / 60) * @Minutes)
Second, I think you can simplify your formula by changing it to the following:
1. @SellPrice_ton - @dsiposal_cost + (@Haul_Marg_doll / @Ton_Estimate)
Divided by
2. @dsiposal_cost
Plus
3. (@Fully_Loaded / 60) * @Minutes
This is purly a mathemathics change and doesn't affect the outcome.
Your formula in InfoPath would then be:
((@SellPrice_ton - @dsiposal_cost + (@Haul_Marg_doll / @Ton_Estimate)) / @dsiposal_cost) + ((@Fully_Loaded / 60) * @Minutes)
I have attached an InfoPath form with both formulas so that you can test both outcomes.
Hope it helps.