Which sentence is better? I was busy to be able to consider the contract and fully read it in detail. Whether you were able to consider the contract, etc. is irrelevant. The issue is whether you did consider the contract, etc.
I was too busy to consider and fully read the contract in detail.
My preference would be, 'I was too busy to read the contract and consider it fully.'
One assumes you are going to read the contract before you consider it.