Is the old VHF antenna still up or still mountable? If so, you're not going to get any better VHF performance with a new antenna. Buy a maximum-gain UHF antenna like the Antennas Direct XG-91 and combine it with your existing antenna using the 7777 preamp.
According to your report, even with the XG-91, reception is likely to be off-and-on. Check with the fine folks at DigitalHome
here to get their opinion on whether this will be worth your while. Good Luck.