Do you have datasheet of the receiver module? What type of the output circuit your receiver provides?

Some more information is required to diagnose the problem.

1) Remove all the buffers and connect the receiver output directly to the INT pin of micro.

2) What is the difference between the (idle state)output of the receiver module when there is micro in circuit and when it out of circuit? Does it remain at +5V in both cases or it falls down when you insert the micro?

Now some test with key press on the remote

3) With 2-3 feet, is the signal quite normal with full 0-5V swing when you press a key on the remote?

4) With 8 feet, is there any swing at all? If yes, what is the voltage range?

Try decreasing the 100K pull-up to some 10K value. If no success, change the receiver module.