hey, i have an old chev and i was wondering how fast i can take it on the highway for long trips. it's a 90 c10, regular cab, long box, with 4.3 / sm465 / 10 bolt w/ 3.08s and 235/75/15 tires (29" tires) it didn't come with a tach for whatever reason. what is the maximum safe rpm of this truck? what does that translate to in speed? i only drive about 100 kph (62 mph) now. can i go faster? i don't want to ruin the motor, i can't afford another one.