I have a 1999 Suzuki GS500E. OCCASSIONALLY it seems to bog-down while riding. While staying steady on the throttle it will slow down as if it’s not getting gas or running out of gas. Throttling while this is happening will make the bike either slow down more or lurch like its finally responding to the added gas. It occasionally stalls because of this issue. I’ve drained the tank, added fresh gas and additive (sea-foam to gas), checked the fuel lines for clogs, checked air filter, changed spark plugs, changed oil and filter. I bought the bike a few weeks ago with 3760 miles on it and I put almost 200 miles on it. I noticed when draining the tank that the inside of the tank has been repaired (resealed with some red-colored sealant).
It’s now at a repair shop for the second time in two weeks (first time they couldn't find the problem and just adjusted the pilot screws and idle).
Can you help?! I’m frustrated and a-bit sad

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