help! choking on a safari

[wulf]

advice time again peeps! need help from the gurus before i bring it to the shop.
ride's a 95 safari, local, manual. had a project in cagayan late last week, took it on a 10-12hour drive (wasn't the one driving, client provided one). on our way back to manila, car shook vigorously on 4th gear, lasted for around 10-15 secs. didn't really happen again after that (til last sunday when i was on edsa). driver said it could be the fuel injectors, 'nasasakal' daw. i also discovered that the rubber tube connected to the racing filter i had installed was 'sucked in' and kinda warped na due to the heat. car's also exhibited a noticeable increase in black smoke the past weeks. hope it's not time for an overhaul some folks suggested a compression test. any thoughts as to what could be the problem? want to know before i bring it to the shop para di ako magoyo. don't worry, i won't be bringing it to Rapide! hehe