You say you have an old basket and a new basket now? An interesting experiment would be to start drilling 1/4" holes in the old basket.. or new basket you choose. Start with 10 or so and test to see if it primes, if not keep going until its swiss cheese and see if it eventually primes. If it eventually does, maybe your pump has a suction problem, it only has enough power to prime if there is little or no obstructions.