few questions aboutm 1990 to 1993 engine swap

I have a 93 1500 single cab stepside that had a 4.3 v6 in it and everything worked fine. WHen i changed over to a 1990 5.7 v8 the speedo/tach/odometer stopped working and i have a horrible voltage problem i changed everything including motor transmission wiring harness and computer. The voltage is fine at around 14(should be at 14.4) until u turn the lights on and other various things that drain power. I have a yellow top optima and a 140 amp alternator so im thinking its a bad ground, does anyone know excatly how many motor grounds there are and if so can u tell me where they should be when i swapped motor i hooked all of them up i thought but could be mistaken. shouldnt there be a ground that hooks into the firewall?? please help!

there should be a ground wire that comes off the back of one of the heads and hooks straight into the firewall...this wire is usually visible just by looking at the rear of the heads.

I have a 93 1500 single cab stepside that had a 4.3 v6 in it and everything worked fine. WHen i changed over to a 1990 5.7 v8 the speedo/tach/odometer stopped working and i have a horrible voltage problem i changed everything including motor transmission wiring harness and computer. The voltage is fine at around 14(should be at 14.4) until u turn the lights on and other various things that drain power. I have a yellow top optima and a 140 amp alternator so im thinking its a bad ground, does anyone know excatly how many motor grounds there are and if so can u tell me where they should be when i swapped motor i hooked all of them up i thought but could be mistaken. shouldnt there be a ground that hooks into the firewall?? please help!

yes I believe on the passenger side cylinder head you should have a ground strap that runs from the head to the firewall.